Washington (AFP) - US President Joe Biden faced a critical test of support for his faltering reelection bid Tuesday as Democrats in Congress met to discuss whether he should stand down in the battle against Donald Trump.

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 weighing up his future.

The leader of the Democratic minority in the US House, Hakeem Jeffries, first huddled with members from competitive districts where the crisis over Biden’s age and health – exacerbated by his disastrous debate performance against Trump – threatens their seats in November.

Jeffries, who said on Monday he still supports the embattled president, then gathered the full Democratic caucus – with US media saying phones are banned to prevent real-time leaks.

Senate Democrats will also discuss Biden’s candidacy at a regular lunch on Tuesday.

Most top Democrats have so far publicly rallied behind Biden but the party remains divided over a catastrophic 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.”

However Jerry Nadler, the ranking Democrat on the House Judiciary Committee, backed Biden despite having reportedly said in a leadership call 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,” he told reporters.

The crisis, and the divisions it has caused among Democrats, has upended the party during a crucial period of the Biden reelection fight, less than four month 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.

- ‘Embarrassing himself’ -

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

The oldest-ever US president in history has dismissed his debate performance, in which he stumbled over words and stood with mouth agape, as a “bad night” caused by a cold and jetlag from arduous foreign travel.

The White House also weighed in, with Biden’s personal doctor saying Biden was seen by a specialist in Parkinson’s disease purely as part of normal neurological examinations during his annual medical.

Biden will address fellow NATO leaders at 5:00 pm (2100 GMT) in a speech closely watched both domestically and by international allies who fear a return of the isolationist Trump.

But Biden’s attempted relaunch failed to convince the editorial board of The New York Times newspaper.

In a scathing piece, the Times board said Democrats “must speak the plain truth” to the president from the grassroots to the highest levels.

“They need to tell him that his defiance threatens to hand victory to Mr Trump. They need to tell him that he is embarrassing himself and endangering his legacy,” it said.

Biden consistently trails in polls, and the media focus is now trained firmly on his own frailties, instead of on his rival’s criminal convictions and proclamations that he wants to be a dictator for a day.

Trump himself broke days of uncharacteristic silence since the debate when he told Fox News on Monday that he thought Biden would resist the pressure and stay in the race.

“He’s got an ego and he doesn’t want to quit,” the 78-year-old former president said.