Democrats face pressure to reveal if they back Biden as Congress reconvenes

Joe Biden told Democrats questioning his leadership to “challenge me at the convention” and sent a combative letter to Congress defending his embattled candidacy on Monday as Washington braced for what may be one of the most politically significant weeks in recent memory.

The US president went on a redoubled counter-offensive as Congress prepared to reconvene after a two-week break, with leading Democratic lawmakers facing the urge or obligation to reveal openly if they plan to stick with him as their nominee for re-election.

Related: Leading House Democrat Adam Smith calls on Biden to end presidential bid

Biden gave a surprise live interview to MSNBC’s Morning Joe – reportedly one of his favourite TV shows – to bolster his letter to returning congressional Democrats, both carrying the unambiguous message that he intended to fight on.

He pledged not to back down even as pressure continued to mount after some prominent House Democrats reportedly told the House minority leader, Hakeem Jeffries, in a virtual meeting that they believe the president should step aside in the race after his poor debate performance against Donald Trump and an underwhelming ABC interview.

“Challenge me at the convention,” he told the show’s joint hosts, Joe Scarborough and Mika Brzezinski, adding that the entreaties to step down had irked him.

“I’m getting so frustrated by the elites, I’m not talking about you guys, but about the elite in the party.”

The defiant posture came as the Senate and House of Representatives both prepared to enter session in Washington simultaneously for the first time since the 27 June debate, during which Biden struggled to make his points, became muddled and could not effectively parry a litany of attacks and lies from the former president.

This drew renewed scrutiny to Biden’s ability to serve as president for another four years as, at 81, he is already the oldest president in US history and had been suffering in the polls over questions over his mental fitness and stamina.

In his letter to Congress, Biden acknowledged these concerns but stressed that they had not weakened his resolve.

“Now that you have returned from the July 4 recess, I want you to know that despite all the speculation in the press and elsewhere, I am firmly committed to staying in this race, to running this race to the end, and to beating Donald Trump,” he wrote.

Referencing “extensive conversations” with the party leadership and rank-and-file members, he acknowledged their “good faith” concerns and fears over the high stakes in the rematch against Trump.

But he added: “I know better than anyone the responsibility and the burden the nominee of our party carries.

“I can respond to all this by saying clearly and unequivocally: I wouldn’t be running again if I did not absolutely believe I was the best person to beat Donald Trump in 2024 … I have no doubt that I – and we – can and will beat Donald Trump.”

His redoubled offensive – following a spate of weekend campaigning events and several interviews, including the high-profile ABC conversation on Friday – came amid fierce speculation that the return of lawmakers to Capitol Hill would intensify pressure on the party leaders who are known to be influential with Biden. These include the Senate majority leader, Chuck Schumer, the former speaker of the House Nancy Pelosi and the South Carolina congressman James Clyburn, as well as Jeffries. Rumors are swirling about which might signal definitively whether they think Biden should stay in the race or step aside.

“I think that he’s got to go out there this week and show the American public that he is still that Joe Biden that they have come to know and love. I take him at his word. I believe that he can do it, but I think that this is a really critical week. I do think the clock is ticking,” the Democratic senator Chris Murphy of Connecticut told CNN on Sunday morning.

Biden attempted to address concerns that he is no longer the campaigner of old in response to Brzezinzki, who asked him how could ensure there would be no repeat of his lamentable debate performance.

“Look at my career: I have not had many of those nights. It was a terrible night, and I really regret it happened,” he said, before appearing to mangle his words.

Addressing calls for him to take a cognitive test, he added: “I had a physical neurological physical as well in February, it’s released. I released all my records, all of them all, and I have a neurological test every single day. Try sitting behind this desk and making these decisions.”

Biden’s message of defiance was amplified by his wife, Jill Biden, at a campaign event for military veterans in Wilmington, North Carolina.

The first lady, branded “Lady MacBiden” by rightwing critics who claim she is manipulating her husband to hold on to power as his powers are supposedly waning, said she was “all in” with his determination to maintain his candidacy.

“For all the talk out there about this race, Joe has made it clear that he’s all in,” she told a cheering crowd that chanted “four more years” in response.

“That’s the decision that he’s made. And just as he has always supported my career, I’m all in too.”

The interview and letter Monday amounted, in part, to a riposte to reports emerging from Sunday’s virtual meeting with between senior Democratic congressmen and Jeffries, suggesting that Jerry Nadler of New York and Jamie Raskin of Maryland were apparently among a significant clutch of lawmakers arguing that Biden should leave the presidential race, with the New York Times reporting this was the consensus. Jeffries has not revealed his hand.

In the days since the debate and ABC interview, a small number of Democratic representatives have openly called on Biden to step down, and other reports emerged that the Virginia senator Mark Warner was looking to assemble a group of Democrats from the upper chamber to encourage Biden to quit his crisis-hit campaign.

Warner reportedly planned a key private meeting for senators on Monday but is now more likely to convene smaller-scale conversations after too much public attention, the Associated Press reported late on Sunday.

Biden spent Sunday campaigning in Pennsylvania, where the Democratic senator John Fetterman likened Biden’s struggles to his own recovery from a stroke and said: “I know what it’s like to have a rough debate, and I’m standing here as your senator.”

Biden insisted to supporters in Philadelphia that he was the person to reunite America in a second term. Last Friday he told ABC his debate performance was “a bad night”, while downplaying the importance of his low approval ratings.

But there were more questions on Sunday and those will only mount this week.

“The interview didn’t put concerns to rest. No single interview is going to do that,” the Democratic congressman Adam Schiff, who is expected to win election as a senator in California in November, said on NBC News.

Related: Biden insists he can reunite US as high-profile Democrats reportedly want him to quit race

“Either he has to win overwhelmingly, or he has to pass the torch to someone who can. It’s as simple as that.”

Schiff said the vice-president, Kamala Harris, could beat Trump decisively and some House lawmakers reportedly also told Jeffries in their virtual meeting that Harris was the most likely person to take over the nomination. The House Democratic caucus met in person on Tuesday.

The last president to decline to seek re-election was Lyndon B Johnson, who abandoned his campaign in 1968 amid the carnage of the Vietnam war, slumping approval ratings and concerns about his own health.