Washington DC - Joe Biden's faltering re-election bid received some much-needed support from senior Democrats on Tuesday, even as the party's lawmakers fell short of reaching a consensus on keeping the president as their 2024 White House nominee.

While the 81-year-old tries to shore up his international reputation in a speech at the NATO alliance's 75th-anniversary summit in Washington, his own party is in crisis mode, weighing whether to jettison Biden as their election candidate.

The leader of the Democratic minority in the US House, Hakeem Jeffries, huddled with members from districts where fears over Biden's age – exacerbated by his disastrous debate performance against Donald Trump – threatened their seats in November.

One participating lawmaker, speaking to US media on condition of anonymity, described the meeting as "intense," with another member saying the mood was "pretty much unanimous" that Biden should step down.

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But in the party's full caucus meeting later Tuesday there were signs that Biden was able to firm up some support, with several lawmakers walking past rows of reporters and declaring their allegiance to the president.

Jerry Nadler, the ranking Democrat on the House Judiciary Committee, backed Biden despite having reportedly said at the weekend that he should step aside.

"He said he's going to remain in, he's our candidate, and we're all going to support him – hopefully, we're all going to support him," Nadler told reporters.

Biden is committed to serving a full second term if reelected, the White House Press Secretary Karine Jean-Pierre said Tuesday.

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The president spoke by phone with the influential Congressional Black Caucus late Monday, and the grouping's vice chair, House Democrat Troy Carter, concluded that "this president is ready, and we stand with him."

Senate Democrats were also discussing Biden's candidacy.

Most top Democrats have so far publicly rallied behind Biden, but the party remains divided over a debate performance watched by some 51 million Americans.

"He just has to step down," House Democrat Mike Quigley told CNN on the way into Tuesday's meeting. "The fighting spirit and pride and courage that served the country so well four years ago helped Joe Biden win, will bring the ticket down this time."

The question of Biden's health and the divisions it has caused among Democrats have upended the party during the re-election fight less than four months before the vote.

"I don't think I've ever been in a more complicated political environment in my life," Senator John Hickenlooper of Colorado said at a breakfast meeting for the NATO summit.

Biden has stepped up his fightback this week, saying he was committed to staying in the race and daring Democratic critics to challenge him at the party convention in August.

Biden consistently trails in polls, and the media focus is now trained firmly on his own frailties instead of on his rival.