Joe Biden was headed for the battleground state of Michigan on Friday, to campaign both for re-election and for his survival as the Democratic presidential nominee. In Washington, calls for the 81-year-old president to quit continued, while the Democratic leader in the House of Representatives said he had discussed the issue with Biden on Thursday, after Biden’s press conference following the Nato summit. In a letter to colleagues, Hakeem Jeffries of New York said discussions about Biden’s age and fitness for office had been “candid, clear-eyed and comprehensive”. “On behalf of the House Democratic caucus,” he said, “I requested and was graciously granted a private meeting with President Joe Biden. “That meeting occurred yesterday evening … I directly expressed the full breadth of insight, heartfelt perspectives and conclusions about the path forward.” Biden’s response was not disclosed, nor details of Democratic “conclusions”. But as the letter was released, an 18th congressional Democrat said Biden should let someone else face Donald Trump, the presumptive Republican nominee, in November. The 19th Democrat to say Biden should go, Mike Levin of California, was reported by Politico to have told the president so to his face on Friday, during a virtual meeting with the Congressional Hispanic caucus. Levin then stated his position publicly. Politico also quoted a “pro-Biden Democrat who attended the meeting” as saying the president “sounded very lucid, sharp, engaged”. There was further worrying news for Democrats when the New York Times reported that so long as Biden remains the nominee, major donors will put on hold “roughly $90m in pledged donations”. The Sunrise Movement also called for Biden to quit. Aru Shiney-Ajay, executive director of the youth-led climate-focused activist group, said she was “concerned Joe Biden isn’t in a position to mobilise young voters and win”. As Biden headed for Detroit, the capital remained abuzz. At the Nato summit on Thursday, Biden spoke assertively and showed his foreign policy experience but also made embarrassing slips, introducing Volodymyr Zelenskiy of Ukraine as “President Putin” and referring to Kamala Harris, his vice-president, as “Vice-President Trump”. Trump seized on that, posting on social media: “Crooked Joe begins his ‘Big Boy’ press conference with, ‘I wouldn’t have picked Vice-President Trump to be vice-president, though I think she was not qualified to be president.’ Great job, Joe!” Biden had appeared to say: “Look, I wouldn’t have picked Vice-President Trump to be vice-president [if] I think she’s not qualified to be president.” Online, Biden fired back, posting: “By the way: Yes, I know the difference. One’s a prosecutor, and the other’s a felon.” Trump, 78 and facing questions about his own cognitive fitness, was convicted on 34 charges arising from hush-money payments to an adult film star. He faces 54 other criminal charges, concerning election subversion and retention of classified information, and was fined millions of dollars in civil cases over business fraud and defamation arising from a rape allegation a judge called “substantially true”. Harris came to prominence as a prosecutor in San Francisco before becoming attorney general of California, a US senator and Biden’s running mate. Michigan is a swing state, choosing Trump in 2016 and Biden in 2020, its Black voters a key part of Biden’s support. The Oscar-winning actor Octavia Spencer was set to appear with Biden in Detroit on Friday. Biden’s campaign said he would target Project 2025, a policy plan led by the Heritage Foundation, a rightwing thinktank. Trump has tried to disavow the project, which Democrats say shows his extremist agenda. There was good news for Biden on Friday: a poll showing him improving since the disastrous debate against Trump in Atlanta that pitched Democrats into crisis. “Biden actually gained a point since last month’s survey, which was taken before the debate,” wrote Domenico Montanaro of NPR, which carried out the poll with PBS and Marist. “He leads Trump 50%-48% in a head-to-head matchup. But Biden slips when third-party options are introduced, with Trump [leading] 43%-42%.” But Politico noted telling dissonance in responses to Biden’s Nato performance. One unnamed Biden aide said the president exceeded expectations and had some great lines. A Democratic aide said Biden had “lowered the bar … until it’s on the floor”. Jim Clyburn of South Carolina, the dean of the Congressional Black caucus, told NBC Biden “sometimes mangles words and phrases but all of that is almost natural for people who grew up stuttering”. He added: “He has one of the best minds that I have ever been around … and so I would hope that we would focus on the substance of this man … and how he has run this country. “… The conversation should focus on the record of this administration, on the alternative in this election, and let Joe Biden make his own decisions about his future. “If he decides to change his mind later on then we will respond to that. We have until 19 August to open our convention” in Chicago. Asked “Is this the same Joe Biden that we saw four years ago?”, Clyburn said: “No!” “I’m not the same Jim Clyburn that I was four years ago and in 10 days I’ll be 84. But I’m a bit wiser than I was before … It’s biblical. When I became a man I put away childish things. Joe Biden has put away childish things because he has become a man. His opponent [Trump] is still a child.” Biden, Clyburn said, “knows what a democracy is all about.”