President-Elect Donald Trump's nomination of Sen. Marco Rubio as his secretary of state, arguably the world's most important diplomat, could change the dial when it comes to the U.S.' relationship with both its enemies and its allies.

Rubio, considered a foreign policy hawk, has been intensely critical of China and Iran, which are considered the U.S.' top economic and geopolitical adversaries, but has also been ambivalent about ongoing support for Ukraine, echoing Trump's stance that the war with Russia must come to an end.

Serving as the vice-chair of the Senate Intelligence Committee and member of the Foreign Relations Committee, Rubio was officially tapped to be secretary of state by Trump late Wednesday as he appointed his top team for the White House following his decisive election win last week.

"He will be a strong Advocate for our Nation, a true friend to our Allies, and a fearless Warrior who will never back down to our adversaries," Trump said in a statement on his Truth Social platform.

Rubio's nomination, along with his assertive position on foreign policy matters and criticism of America's rivals, could ease concerns among U.S. allies that the world's most powerful economy retreat from the global stage, given Trump's "America First" policy.

Ahead of his nomination, and after Trump's election win, Rubio told CNN that the U.S. was entering "an era of pragmatic foreign policy."

"The world is rapidly changing. You know, adversaries are uniting — in North Korea, Iran, China, Russia — [and] increasingly coordinating," Rubio said. "It is going to require us to be very pragmatic and wise in how we invest overseas and what we do."

The relationship between Trump and Rubio has not always been easy. Both men ran for president in 2016, bitterly clashing as they campaigned for the Republican nomination with Trump describing Rubio as "Little Marco," and Rubio making fun of Trump's "small hands."

At that time, Rubio was critical of Trump's isolationist foreign policy stance. Back in 2016 he said "the world without American engagement is a world none of us wants to live with," arguing against Trump's position that the U.S. gives more than it gets from its interactions with the international community.

Rubio has since made peace with the president-elect, however, backing him in his presidential campaign.

Rubio's office did not immediately respond to a request for comment as to his new role, but here's a snapshot of the 53-year-old politician's comments on some of the U.S.' biggest foreign policy challenges, signaling what we might expect from the incoming secretary of state:

Sen. Rubio is a renowned hawk when it comes to China, aligning him closely with President-Elect Trump who has vowed to redress trade imbalances with Beijing, firstly by promising to impose tariffs on Chinese goods of 60% or higher, once in office.

That policy is likely to find favor with Rubio, whose Senate biography describes him as "leading the charge to rebalance our relationship with Communist China." Rubio has been highly critical of China's economic power base, stating in his most recent report on the country's industrial policy that "through theft, market distorting subsidies, and strategic planning, Beijing now leads in many of the industries that will determine geopolitical supremacy in the 21st century."

"This report should serve as a wakeup call to lawmakers, CEOs, and investors," Rubio said, calling for "a whole-of-society effort to rebuild our country, overcome the China challenge, and keep the torch of freedom lit for generations to come."

There's no love lost for Rubio in Beijing. In 2020, Rubio and other top U.S. officials were sanctioned by China during a round of tit-for-tat sanctions by Beijing and Washington.

It's uncertain how a Trump administration, and future Secretary of State Rubio, will approach Iran with both Republicans giving off mixed signals when it comes to a punitive or more pragmatic policy stance.

Trump caused international consternation in his first term in office by ripping up the Iran nuclear deal in 2018 and re-imposing biting sanctions on Iran, with critics warning that Iran's nuclear weapons capability would be achieved sooner rather than later, as a result.

Ahead of his election win last week, Trump signaled he was open to reaching a new nuclear agreement with Iran, however, telling reporters in New York, "sure, I would do that." "We have to make a deal, because the consequences are impossible. We have to make a deal," he said, in comments reported by Politico.

For its part, Iran's President Masoud Pezeshkian said Tuesday that the country "will have to deal with the U.S. in the regional and international arena," Reuters reported, signaling Iran could also be open to talks.

A new nuclear deal might not go down well in Israel, however, a country Trump cast himself as a "protector" of during his election campaign. Rubio too has been a vocal critic of Iran and a staunch supporter of Israel as it continues its attacks on Iranian proxies, the militant groups Hamas and Hezbollah, in Gaza and Lebanon, respectively.

In late September, Rubio gave his backing to the Israeli airstrike that killed Hezbollah's leader, Hassan Nasrallah, telling NBC News that "Israel has no choice but to defend itself. Wiping out not just Nasrallah, but the senior leadership of this evil organization, I think, is a service to humanity."  He also said Iran's goal in the Middle East was to "seek to drive America out of the region and then destroy Israel."

Rubio has not ruled out taking a pragmatic approach to Tehran either, telling NBC News that "if the Iranian regime tomorrow said, 'We're going to stop trying to become the regional power, we're going to stop our nuclear weapons, we're going to stop sponsoring terrorism, we're going to stop trying to kill you —which is what they're trying to do with Donald Trump — we're going to stop all of these things,' theoretically, yes. Of course, you could work something like that out."

Still, he added that the scenario was "unlikely because that's the very driving mission and purpose of the regime." Iran has denied U.S. charges that Tehran was linked to an alleged plot to kill Trump.

It's widely agreed that the incoming Trump administration will be far more hostile toward granting Ukraine more military aid, significantly inhibiting its ability to continue to fight back against Russia. It's also seen as likely that a Republican administration will push Kyiv into peace talks with Russia in which it will be forced to concede occupied land to its neighbor as part of a peace deal.

Rubio has insisted he is "not on Russia's side" but he told NBC News in late September that "unfortunately the reality of it is that the way the war in Ukraine is going to end is with a negotiated settlement."

"We hope that when that time comes, there is more leverage on the Ukrainian side than on the Russian side. That really is the goal here, in my mind. And I think that's what [former President] Donald Trump is trying to say," Rubio said.

The senator was initially a vocal supporter of Ukraine but his, and other Republicans' backing has waned as the funding bill has racked up after 32 months of war, and as domestic issues remain unresolved.

Rubio was among a small group of hardline Republicans that voted in April against a $95 billion aid package to help Ukraine, Taiwan and Israel, saying he opposed the bill because the U.S. was not doing enough to tackle its own domestic challenges, such as border security and immigration.