Joe Biden's faltering reelection 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.

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

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 -- threaten 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.

"He just has to step down," House Democrat Mike Quigley told CNN on the way into Tuesday's meeting.

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.

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.