Former President Barack Obama and Vice President Kamala Harris have been in close touch since she announced her presidential candidacy Sunday, having multiple conversations this week as she kicks off her campaign, according to four people familiar with their discussions.

Obama privately has fully supported Harris' candidacy and plans to endorse her soon, these people said.

"He has been in regular contact with her and thinks she's been off to a great start," one of them said.

Obama is one of the only high-profile Democrats in the country who has yet to endorse Harris. While other party leaders have stepped forward to publicly back her, he has so far kept his support private.

The people familiar with the discussions didn't know the precise timing of his endorsement. One of them said Obama didn't want it to overshadow President Joe Biden's moment, particularly his Oval Office address to the nation Wednesday night.

Another person familiar with the discussions said Obama and Harris, who is seeking to maintain the momentum her campaign has enjoyed among Democrats since she entered the race, wanted his endorsement to stand as its own moment.

Aides to Obama and Harris also have discussed arranging for the two of them to appear together on the campaign trail, though no date has been set, three of the people familiar with the discussions said.

Michelle Obama also supports Harris' candidacy, two people familiar with the matter said.

"President Obama looks forward to helping Democrats up and down the ballot make the case to voters this fall," said Eric Schultz, a senior adviser to Obama. "Our strategy will be based on driving impact, especially where and when his voice can move the needle."

During their conversations in recent days, Obama has offered Harris his counsel on setting up a campaign and on other aspects of mounting a successful bid for the White House, which he has done twice, the people familiar with their discussions said.

From Obama's perspective, Harris has taken on a lot in a very short time, and he sees himself as a resource and a sounding board for her as she navigates a high-stakes campaign with about just 100 days until Election Day, according to two of the people familiar with their discussions.

Obama views his utility in the campaign as helping unify his party and moving Democrats forward, and he's expected to be a fixture on the campaign trail this fall.

The only publicly known phone call between Obama and Harris took place Sunday, when Biden announced he was ending his re-election campaign and swiftly endorsed Harris.

Obama issued a statement Sunday praising Biden and supporting a process to select a new Democratic nominee, but he didn't endorse Harris.

"We will be navigating uncharted waters in the days ahead," Obama said in the statement. "But I have extraordinary confidence that the leaders of our party will be able to create a process from which an outstanding nominee emerges."

Harris then quickly received endorsements from across the country, and no one has stepped up to challenge her for the nomination.

Since Biden's June 27 debate performance, Obama had privately expressed concerns about his former vice president's ability to defeat former President Donald Trump in November, NBC News has reported. He didn't publicly or privately urge Biden to remain in the race, though he defended his debate performance by writing on X that he understood what it was like to have a poor presidential debate.

Obama and Harris have known each other for years. She was an early supporter of his 2008 campaign and was given a speaking role at his 2012 nominating convention. Obama campaigned for Harris when she was running for attorney general in California and supported her when she ran for the Senate in 2016.