Two witnesses told NBC News there was a lack of safety measures beyond the rally's security perimeter.

Despite having tickets to attend the rally, Valerie Fennell and Deb Kuminkoski decided to watch the rally from Fennell's backyard to avoid the large crowd and heat. Her backyard was between where the crowd gathered and the AGR factory where the shooter was camped on a roof.

In hindsight, Fennell said she was in disbelief that she was not contacted ahead of the rally.

"The entire area just outside the event's perimeter was open and people were walking around freely within 150 yards of where Trump was speaking with no security visible," the two women told NBC.

Read the full report in NBC News.

— Charmaine Jacob

Biden will to return to the campaign trail this week, which includes a keynote speech at the NAACP convention in Las Vegas on Tuesday.

The president's planned trip to the LBJ Presidential Library in Austin on Monday has been postponed.

Although no new date has been announced, Mark Updegrove, president and CEO of the LBJ Foundation, said the visit could happen in the coming weeks.

"We are honored President Biden remains committed to joining us at the LBJ Library to mark the 60th Anniversary of the Civil Rights Act and we look forward to hosting him later this month," Updegrove said on X.

— Charmaine Jacob

Trump's support base is "very much consolidated" entering the Republican National Convention and would have been even without the attempted assassination, said former U.S. Ambassador to Singapore David Adelman.

Adelman told CNBC's "Squawk Box Asia" that he expects the attempted assassination to be "a subject for discussion over the entirety of the campaign."

"These are very uncommon occurrences in the United States, and I think Americans are rightfully traumatized by what has occurred," he said.

—Lee Ying Shan

Trump said his speech at the Republican National Convention will now focus on national unity, instead of targeting Joe Biden's policies.

The former president told the Washington Examiner "he wanted to take advantage of a historic moment and draw the country together."

"Honestly, it's going to be a whole different speech now," he said in an interview following the assassination attempt against him. Trump's speech is slated for Thursday.

The former president also explained that holding his fist in the air despite blood trickling down his face was a sign to show people that he was fine, and "that America goes on, we go forward, that we are strong."

— Charmaine Jacob

Trump has arrived in Milwaukee for the Republican National Convention where he is expected to be nominated as the Republican presidential candidate.

The former president was initially going to delay the trip by two days due to the attempted assassination, but decided otherwise.

"I was going to delay my trip to Wisconsin, and The Republican National Convention, by two days, but have just decided that I cannot allow a 'shooter,' or potential assassin, to force change to scheduling, or anything else," the former president wrote on social media platform Truth Social.

The four-day convention kicks off on Monday.

— Lee Ying Shan

President Joe Biden in a rare Oval Office address responded to the assassination attempt against former President Donald Trump by condemning violence and urging Americans to cool down their inflamed political discourse.

"We can't allow this violence to be normalized," Biden said. "You know, the political rhetoric in this country has gotten very heated. It's time to cool it down."

The shooting "calls on all of us to take a step back, take stock of where we are, how we go forward from here," Biden said in the speech, which lasted less than seven minutes.

Watch the entire address below:

— Kevin Breuninger

Biden ended his Oval Office address by stressing that democratic norms of decency, dignity and fair play are more than just "quaint notions," but "living, breathing realities."

"Look, let's never lose sight of who we are," Biden said.

"Let's remember we are the United States of America. There is nothing, nothing, nothing beyond our capacity when we do it together," he said. "God bless you all, and may God protect our troops."

Biden spoke for less than seven minutes.

— Kevin Breuninger

Biden's Oval Office address tonight was his third since taking office. It is the seventh time in his presidency that he has delivered an address in primetime, not including his State of the Union addresses.

His most recent primetime address from the Oval Office before Sunday was on Oct. 19, 2023, when Biden delivered remarks on the Israel-Hamas conflict.

– Josephine Rozzelle

Biden condemned political violence in all its forms, declaring that the natural disagreements that arise in a free country must never devolve into a "killing field."

"Disagreement is inevitable in American democracy. It's part of human nature," Biden said. "But politics must never be a literal battlefield or, God forbid, a killing field."

Biden's speech invoked not just the assassination attempt against Trump but also the attack on Paul Pelosi, the husband of former House Speaker Nancy Pelosi; the Jan. 6, 2021, Capitol riot; and other events.

— Kevin Breuninger

President Joe Biden said at the start of his national address that he wanted to speak about "the need for us to lower the temperature in our politics."

Biden began speaking from the Oval Office at 8:01 p.m. ET.

— Kevin Breuninger

President Biden is set to deliver remarks from the Oval Office at 8 p.m. ET, where he will make a plea to end political violence in light of the assassination attempt on former President Donald Trump, a Biden campaign official previewed to NBC News.

Throughout his campaign, Biden has repeatedly condemned examples of political violence like the 2017 Charlottesville riots and the Jan. 6 Capitol insurrection, both of which he has at least in part blamed Trump for inciting.

"He has been clear that we don't settle our differences through violence," the Biden campaign official told NBC News. "We settle them at the ballot box."

In the hours since the Trump assassination attempt, some Republican lawmakers have blamed Biden's campaign rhetoric for the shooting.

The campaign official staunchly rejected that notion: "In a moment when Americans should come together and unite to condemn this horrifying attack, anyone – especially elected officials with national platforms – politicizing this tragedy, spreading disinformation, and seeking to further divide Americans isn't just unacceptable – it's an abdication of leadership."

The official said Biden will continue to "draw the contrast" with Republicans' agendas throughout the rest of the week, as the Republican National Convention is in full swing.

After tonight's address, Biden will sit for an interview with NBC News' Lester Holt on Monday.

— Rebecca Picciotto

Democratic donor and LinkedIn co-founder Reid Hoffman penned a lengthy X post Sunday afternoon wishing former President Donald Trump a speedy recovery and clarifying a previous comment he made from Sun Valley, Idaho, on Trump being a martyr.

"At a recent business conference, Peter Thiel said that my lawsuit work against Trump was "turning a clown into a martyr." In that context, I replied that I wished that Trump would martyr himself - meaning let himself be held accountable - for his assaults on and lies about women," Hoffman wrote.

"Of course I meant nothing about any sort of physical harm or violence, which I categorically deplore."

Hoffman previously provided financing to E. Jean Carroll's legal efforts against Trump. The two civil trials resulted in a judge ruling that Trump owed Carroll more than $88 million in damages for sexual abuse and defamation.

— Jake Piazza

Donald Trump has landed in Milwaukee, Wisconsin for the Republican National Convention, which will take place Monday to Thursday. Tens of thousands of people are expected to attend.

— Rebecca Picciotto

Senate Minority Leader Mitch McConnell, R-Ky., offered a message of optimism to attendees at a Kentucky delegation event kicking off the Republican National Convention, NBC News confirmed.

"We are not going to let this kind of hatred redefine this country," said McConnell, who attended the event with his wife, Elaine Chao.

"How about that fist pump on the way up," he joked, referencing Donald Trump punching his fist in the air for several seconds as Secret Service rushed him off stage at the rally.

— Rebecca Picciotto

JPMorgan Chase CEO Jamie Dimon addressed the attempted assassination of former President Donald Trump in a memo sent out to all employees.

Dimon said the leadership's teams thoughts go out to Trump, his family and the families of the victims injured or killed Saturday evening.

"We must all stand firmly together against any acts of hate, intimidation or violence that seek to undermine our democracy or inflict harm," Dimon also wrote. "It is only through constructive dialogue that we can tackle our nation's toughest challenges."

— Hugh Son & Jake Piazza

The Pennsylvania State Police identified the three rally attendees who were shot, one who was tragically killed and two who were left in critical condition. All three were Pennsylvania residents.

David Dutch, a 57-year-old resident of New Kensington, and James Copenhaver, a 74-year-old resident of Moon Township, both suffered critical injuries but are now in stable condition, although still hospitalized, according to the police department.

The deceased victim, Corey Comperatore, was a 50-year-old former Pennsylvania firefighter with a wife and two daughters.

Comperatore was identified by Gov. Josh Shapiro earlier Sunday, who had spoken with his family. The governor said his family wanted to let the public know that Comperatore "died a hero" by using his body as a shield to protect them at the rally.

"These victims and their families are certainly in our thoughts today," State Commissioner Colonel Christopher Paris said. "The Pennsylvania State Police continue to work tirelessly alongside our federal, state and local partners as this investigation continues."

— Rebecca Picciotto

The Secret Service will not change its security plan for the Republican National Convention, despite the alleged assassination attempt Saturday.

"There have been no changes to our current operational security plans for this event," Audrey Gibson-Cicchino, the RNC coordinator for the Secret Service, said at a Sunday press conference, adding that the plan has been developed over 18 months and has been designated the highest level of security.

"We are confident in these security plans that are in place for this event and we're ready to go."

Firearms will not be allowed inside the convention, nor within the Secret Service's security perimeter. But outside of that perimeter, just blocks away from the GOP convention, firearms will be permitted.

The convention will take place from Monday to Thursday in Wisconsin, an open-carry state. As a result, the Secret Service said it did not have jurisdiction over firearm regulation outside of its outlined security perimeter and deferred to the state's law enforcement.

"We have to respect the Second Amendment right to carry your firearm," Milwaukee Police Chief Jeffrey Norman said at the press conference. "As that is your right, please exercise your right in a responsible manner."

"The Milwaukee Police Department will not tolerate any particular behaviors outside of what is legally allowed in regards to that right," Norman added.

— Rebecca Picciotto

A Bethel Park rehab facility said that the 20-year old gunman worked as its dietary aide, noting that his background check and job performance had never raised an alarm.

"We are shocked and saddened to learn of his involvement as Thomas Matthew Crooks performed his job without concern and his background check was clean," Marcie Grimm, an administrator at Bethel Park Skilled Nursing and Rehabilitation Center, the suspected shooter's employer, wrote in a statement.

Grimm said that the facility is "fully cooperating" with law enforcement as the FBI continues its investigation.

"We condemn all acts of violence," Grimm wrote.

— Rebecca Picciotto

Moments before the suspected shooter opened fire on former President Donald Trump, a municipal police officer confronted him, said Butler County Sheriff Michael T. Slupe in an interview with The Washington Post.

The officer lifted himself high enough to look onto the roof, Slupe said, and the suspected shooter pointed his gun at the peering officer. Slupe said the officer was holding the edge of the roof, so he was not holding his gun in his hand, and then dropped down.

Moments later, the gunman opened fire on the rally, according to Slupe's account to The Washington Post.

"He lets go because he doesn't want to get killed," Slupe said to The Washington Post.

The officer from the roof was investigating an earlier report of a suspicious individual, according to the Washington Post.

— Jake Piazza

CNBC Squawk Box anchor Joe Kernen spoke with former President Trump on Sunday, according to Kernen's post on X.

"He asked me to pass on to all that he's doing great and is gratified by all the encouragement and support, from both sides of the aisle," Kernen wrote, adding, "He was in amazing spirits, added he has a little problem with his right ear but was glad he turned his head at the last minute."

Kernen called in to MSNBC with Katy Tur shortly afterward and recapped the roughly three-minute conversation.

Trump told Kernen he received calls from both sides of the aisle, including from some people he did not expect to hear from.

— Jake Piazza

The FBI agents investigating the Trump assassination attempt said the suspected gunman acted alone but that there are still many questions that need to be answered.

"At this point the investigation, it appears that he was a lone actor," FBI executive assistant director Robert Wells said during a call with reporters, noting that the investigation is still in its early phases.

Kevin Rojek, the FBI special agent leading the investigation, said that the bureau has confirmed that the suspected shooter used an AR-style 556 rifle, which was purchased legally.

Many questions remain as the investigation continues.

Rojek added that they have not yet "identified an ideology" associated with the gunman and that the FBI is still working to piece together the timeline of the events leading up to the assassination attempt.

The FBI said it had searched the suspected gunman's vehicle and that it is working to get full access to his phone and social media accounts, in order to understand his motive and the sequence of events leading up to the shooting.

During the vehicle search, Rojek said, the FBI found a "suspicious device" that was inspected by bomb technicians. The device is still under analysis.

The FBI officials noted that they are also keeping tabs on the fallout of the events and monitoring the upcoming Republican and Democratic conventions. The FBI said it has not so far identified any existing public safety concerns related to this shooting's aftermath.

Attorney General Merrick Garland and FBI Director Christopher Wray were also on the call and extended their condolences to the shooting victims.

"Our hearts are with them and with those critically injured and their families," Garland said.

Wray said the bureau has dedicated the "full force of the FBI to this investigation." That includes criminal and national security teams, tactical support, teams to process crime scene evidence, victim services, specialists, the FBI lab and its operational technology division, he said.

The FBI officials said it has received over 2,600 tips so far, each of which the bureau plans to investigate. They reiterated that the public should report any knowledge of the situation to their tip line at 1-800-CALLFBI (1-800-225-5324) or online at fbi.gov/butler.

— Rebecca Picciotto

The reported attempted assassination of Donald Trump, just two days before the Republican National Convention kicks off, will likely supercharge the emotional energy of what was already expected to be an intense four-day bout of Trump fanfare.

"When he [Trump] walks in that arena for the first time, the decibel level will be so high it will be almost unmeasurable," Corey Lewandowski, a close Trump ally who is advising the RNC, said Sunday.

Aside from the elevated emotional intensity, the general structure and schedule of the Milwaukee convention is set to remain the same, Wisconsin GOP Chair Brian Schimming said in a press conference, noting that he had spoken with RNC Chair Michael Whatley.

That schedule includes the highly-anticipated announcement of Trump's vice presidential pick, which is expected Wednesday.

In a Truth Social post Sunday, Trump said he was looking forward to addressing the nation from the convention in Wisconsin. Later Sunday, he was en route to the Badger State.

The RNC has over 80 names on its speaker lineup, including former GOP presidential candidate Nikki Haley, who on Sunday accepted her invitation to speak. She appeared to receive that invitation sometime in the past several days, NBC News reported on Saturday.

— Rebecca Picciotto

Trump Media CEO Devin Nunes sent his condolences to the families of the rally attendees who were killed or wounded, extended support to Donald Trump and demanded the federal government conduct a "fast, thorough" investigation of the assassination attempt.

"I thank God President Trump survived the assassination attempt and is now safe," Nunes said in a Saturday statement.

He also called on federal officials to provide "any security resources requested by President Trump to guarantee his safety."

Trump is the majority stakeholder of Trump Media, the parent company of Truth Social.

Nunes punctuated his statement on a note of optimism, saying, "America will overcome this despicable shooting and together, our nation will endure."

— Rebecca Picciotto

Former President Donald Trump will not delay his trip to Wisconsin for the Republican National Convention, where he will officially be named the party's 2024 presidential candidate, according to his post on Truth Social.

"Based on yesterday's terrible events, I was going to delay my trip to Wisconsin, and The Republican National Convention, by two days, but have just decided that I cannot allow a "shooter," or potential assassin, to force change to scheduling, or anything else," Trump wrote.

Trump said he will leave at 3:30 pm Sunday. The Republican National Convention begins Monday in Milwaukee.

— Jake Piazza & Rebecca Picciotto

President Joe Biden said he was grateful for Donald Trump's safety, sent his condolences to the shooting victims and urged the public not to speculate about the gunman's motives.

"I'm sincerely grateful that he's doing well and recovering," Biden said, speaking of the former president.

Biden added that he would continue to ensure that Trump had the necessary Secret Service detail to keep him safe. He and Trump spoke on the phone Saturday evening in a rare one-on-one conversation that the White House told NBC News was short but "respectful."

Biden also extended his condolences to the family of Corey Comperatore, the 50-year-old father and former Pennsylvania firefighter who was killed at the rally. The president also wished the other victims a full recovery.

"There is no place in America for this kind of violence or any violence for that matter," Biden said, reiterating his comments from a Saturday evening presser.

Biden said he ordered the Secret Service to review all security measures for the upcoming Republican National Convention and is asking for an independent review of the security at Trump's Saturday rally. He said he would share that review with the public.

The president also urged the public not to jump to conclusions about the gunman's motives as the FBI's investigation into the attempted assassination is still ongoing.

"Please don't make assumptions about his motives or affiliations," Biden said. "Let the FBI do their job and their partner agencies do their job."

— Jake Piazza & Rebecca Picciotto

It is unclear if the containers and canisters in the suspected shooter's car were explosives, two officials told NBC News.

The motive of Thomas Matthew Crooks, the 20-year-old the FBI believes to be the shooter, is still not known. The preliminary count is that Crooks fired eight shots, though that number could change as the FBI, ATF and other agencies continue looking over the site, an official said.

Crooks' family is cooperating with law enforcement, a senior law enforcement official directly briefed on the matter said.

— Jake Piazza

The suspected shooter, now identified as 20-year-old Thomas Matthew Crooks, maintained a Discord account that the company does not believe was linked to the alleged assassination attempt, a Discord spokesperson told NBC News via email.

The spokesperson added that the account was rarely used.

"We have identified an account that appears to be linked to the suspect; it was rarely utilized and we have found no evidence that it was used to plan this incident, promote violence, or discuss his political views," the spokesperson told NBC News .

"Discord strongly condemns violence of any kind, including political violence, and we will continue to coordinate closely with law enforcement," the spokesperson added.

— Jake Piazza

President Biden is set to speak this afternoon after receiving an updated briefing in the Situation Room with Vice President Kamala Harris and several top security and law enforcement officials.

— Rebecca Picciotto

Democratic Gov. Josh Shapiro of Pennsylvania identified the victim who was shot and killed as firefighter Corey Comperatore.

Shapiro added that he spoke with Comperatore's wife and two daughters who said he "died a hero," diving on his family to protect them as shots were fired.

"Corey was a girl dad. Corey was a firefighter. Corey went to church every Sunday. Corey loved his community," Shapiro said. "Corey was an avid supporter of the former president, and was so excited to be there last night with him in the community."

Along with the killing of Comperatore, the shooting left two civilians critically injured.

The FBI's investigation into the attempted assassination is still ongoing.

— Rebecca Picciotto

President Joe Biden and Vice President Kamala Harris are receiving an updated briefing in the White House Situation Room from top security and law enforcement officials.

In the room with them are Attorney General Merrick Garland, Homeland Security Secretary Alejandro Mayorkas, FBI Director Christopher Wray, National Security Advisor Jake Sullivan, Secret Service Director Kim Cheatle and several others.

Cheatle and Mayorkas, in particular, are facing increasing calls from Congress to provide answers to the public about the security lapses that allowed a gunman to get within shooting range of Donald Trump.

Both the president and the vice president received an initial briefing last night.

Biden delivered on-camera remarks Saturday evening to condemn the political violence and later had a short but "respectful" phone call with Trump, a White House official told NBC News.

— Rebecca Picciotto

As the initial dust of the attempted Trump assassination settles, members of Congress are becoming increasingly vocal about the need for answers on what went wrong.

"The seriousness of this security failure and chilling moment in our nation's history cannot be understated," House Homeland Security Chair Mark Green, R-Tenn., wrote in a letter to Homeland Security Secretary Alejandro Mayorkas.

Green demanded documents regarding the security coordination for the event's perimeter, as well as any messages or correspondence between the Secret Service, DHS or president, and other records of Secret Service protocol.

Green joins a variety of Republican lawmakers looking for answers about Saturday's shooting as rumors abound about what went awry, some of which the Secret Service has debunked directly.

House Speaker Mike Johnson, R-La., said he had been briefed and spoke with Mayorkas on Saturday, though he still has many questions.

House Oversight Committee Chair James Comer, R-Ky., has also invited the Secret Service director for a congressional hearing to testify on Saturday's events.

— Rebecca Picciotto

A GoFundMe page created by Donald Trump's campaign finance director that says it was started for the victims and their families from Saturday's assassination attempt on former President Donald Trump has raised more than $800,000.

Some of the largest donations listed include $50,000 from Kid Rock, $30,000 from Vivek Ramaswamy, $15,000 from Ben Shapiro and $10,000 from investor Bill Ackman. Another $10,000 gift appears to be from Trump's daughter Ivanka Trump and her husband Jared Kushner.

The donations have not been verified by CNBC or NBC News. But Kid Rock, Ramaswamy and Shapiro have all either posted or reposted links to the page on their X accounts.

The GoFundMe page says it was organized Meredith O'Rourke, Trump's national finance director for his 2024 election campaign.

One rally attendee was killed and two others are in critical condition.

— Jake Piazza

Former first lady Melania Trump has broken her silence on the attempted assassination of her husband.

"When I watched that violent bullet strike my husband, Donald, I realized my life, and Barron's life, were on the brink of devastating change," Melania wrote, thanking the Secret Service for their protection.

"A monster who recognized my husband as an inhuman political machine attempted to ring out Donald's passion - his laughter, ingenuity, love of music, and inspiration," she wrote.

"The core facets of my husband's life - his human side - were buried below the political machine. Donald, the generous and caring man who I have been with through the best of times and the worst of times."

It was a rare and emotional statement from the former first lady, who closely guards her privacy and been noticeably absent from Trump's political events since he left the White House in 2021.

Melania Trump sent her sympathies to the families of the victims of the shooting. She also reflected more broadly on the state of division in American politics, and ended her statement on a note of encouragement.

"This morning, ascend above the hate, the vitriol, and the simple-minded ideas that ignite violence," she wrote. "The winds of change have arrived."

— Rebecca Picciotto

Rep. Ruben Gallego, an Arizona Democrat and candidate for the Senate, sent a letter to U.S. Secret Service Director Kimberly Cheatle after last night's assassination attempt on former President Donald Trump.

"This was a security failure at the highest level, not seen since the attempted assassination of President Reagan," wrote Gallego. "This cannot happen, and I demand accountability."

Gallego detailed several questions that he wants answers to, including who approved the security plan and whether surrounding buildings were properly assessed for threats.

— Jake Piazza

President Joe Biden and former President Donald Trump briefly spoke on the phone Saturday evening in a rare one-on-one conversation.

A White House official described the phone call to NBC News as "good, short and respectful."

It was the first time the candidates had spoken to each other since their presidential debate on June 27.

Earlier that evening, Biden delivered brief remarks on camera in Delaware and condemned the political violence, before heading back to Washington.

"There's no place in America for this kind of violence," Biden said Saturday. "It's sick. It's sick."

— Rebecca Picciotto

Former Vice President Mike Pence said he and his wife "thank God" for Donald Trump's safety and sent their condolences and support to the victims and their families.

He added a note of gratitude for the Secret Service's "swift response," which he added, "undoubtedly saved lives."

"There is no place in America for political violence and it must be universally condemned," he added.

Pence was one of several government officials targeted by armed rioters during the deadly Jan. 6 Capitol attack, which he partially blamed Trump for inciting.

— Rebecca Picciotto

More than 12 hours after the shooting, two victims remain in critical condition at a local hospital, authorities and a hospital spokesman said.

The victims' names have not been released, and it was unclear Sunday morning when officials would deliver another update.

One attendee at the rally died on the scene, as did the gunman, who was killed by law enforcement.

— Jake Piazza

Republican House Speaker Mike Johnson blamed incendiary political rhetoric for Saturday's assassination attempt of Donald Trump and reiterated that Congress is launching a full investigation into the incident.

"We can't go on like this as a society," Johnson said in an interview with NBC's "TODAY." "Everyone needs to turn the rhetoric down."

He pointed to President Joe Biden's campaign rhetoric, including remarks on a private donor call in which Biden said, "It's time to put Trump in the bullseye."

"I know that [Biden] didn't mean what is being implied there," said Johnson, "but that kind of language on either side should be called out."

Congress plans to do a full investigation of the shooting, he said, to answer questions about any potential security lapses and "anything else that the American people need to know."

"Lots more questions than answers this morning," he added.

— Rebecca Picciotto

Donald Trump said in a Truth Social post that he was looking forward to addressing the country at this week's Republican National Convention in Wisconsin.

The former president also thanked the public for its support and sent condolences to the shooting victims and their families.

"We will FEAR NOT, but instead remain resilient in our Faith and Defiant in the face of Wickedness. Our love goes out to the other victims and their families," Trump wrote. "I truly love our Country, and love you all, and look forward to speaking to our Great Nation this week from Wisconsin."

The RNC is set to take place in Milwaukee from Monday to Thursday.

Saturday's assassination attempt on Trump will not change the RNC's structure, a senior Republican official involved in the planning told NBC News on Sunday.

The official added that the shooting and Trump's survival could color the convention with more emotional overtones, but that the fundamental plan will not change.

— Rebecca Picciotto

The Secret Service rejected rumors that it had denied Donald Trump's requests for additional security resources.

Secret Service spokesman Anthony Guglielmi said that the notion that Trump's team asked for more security and was rebuffed "is absolutely false."

"In fact, we added protective resources & technology & capabilities as part of the increased campaign travel tempo," Guglielmi wrote in a social media post.

To prepare for more travel and events on the campaign trail, Trump's team beefed up his Secret Service detail with more special agents and teams, an official told NBC News in May.

— Rebecca Picciotto