Unlock the US Election Countdown newsletter for freeThe stories that matter on money and politics in the race for the White HouseA growing number of Democratic lawmakers, including a third US senator, have called for Joe Biden to withdraw from this year’s White House presidential race, deepening the peril for his campaign for re-election. In a joint statement on Friday morning, four US House members — Jared Huffman, Mark Pocan, Chuy Garcia and Marc Veasey — said it was time for the 81-year-old president to “pass the torch to a new generation of Democratic leaders”. “We must face the reality that widespread public concerns about your age and fitness are jeopardising what should be a winning campaign,” the politicians added. House Democrats Sean Casten, Greg Landsman, Zoe Lofgren, Kathy Castor, Betty McCollum, Morgan McGarvey and Gabe Vasquez also called on Biden to drop out on Friday. Meanwhile, New Mexico senator Martin Heinrich became the third Democratic member of the upper chamber of Congress to urge Biden to drop out, joining Jon Tester of Montana and Vermont’s Peter Welch.“This moment in our nation’s history calls for a focus that is bigger than any one person,” Henrich said, adding it was “in the best interests of our country” for the president to end his campaign.Biden insisted on Friday that he would remain in the race, saying in a statement he “look[ed] forward to getting back on the campaign trail next week to continue exposing the threat of Donald Trump’s Project 2025 agenda”. The president has been isolating at his holiday home in Delaware since testing positive for Covid-19 on Wednesday. White House doctor Kevin O’Connor said on Friday that Biden’s symptoms had “improved meaningfully” and he would continue taking Paxlovid, the antiviral drug.The new wave of lawmakers calling for Biden to quit comes as Democratic party grandees such as former House Speaker Nancy Pelosi, as well as the megadonors crucial to funding his campaign, heap pressure on him behind the scenes.The Financial Times reported on Thursday that donors and other senior party operatives believe Biden is very close to a decision to exit the race. On Friday, Michael Moritz, the venture capitalist and Democrat megadonor, called on Biden to step aside, saying the president had a choice between “vanity or virtue” in remarks first reported by The New York Times and confirmed by Moritz. He added that Biden’s attempts to hold on for a second term risked damaging the country, but did not say who he would back to replace him.Chris Coons, the Democratic senator and close Biden ally, said on Friday that the president was getting the necessary advice to make a decision about his political future.“I am confident he is hearing what he needs to hear,” he said while speaking on a panel at the Aspen Security Forum.But Coons — who insisted Biden was “strong” and “capable” enough to carry on — acknowledged the unease within the Democratic party, saying: “There is a lot of concern and anxiety because the stakes are so significant.”The latest interventions came a day after Trump formally accepted the Republican party’s nomination for president, less than a week after he narrowly escaped assassination in Pennsylvania.US Election CountdownSign up to our US Election Countdown newsletter, your essential guide to the twists and turns of the 2024 presidential electionThe former president has surged ahead of Biden in the polls despite his recent criminal convictions, building a lead across the crucial swing states that will decide November’s vote. More than 30 members of Congress have now said Biden needs to drop his re-election bid, a view shared privately by many more who have not yet gone public. But some fear that risks a new split within the party. However, some Democrats, including many progressives, have supported him. Congresswoman Alexandria Ocasio-Cortez used an Instagram livestream in the early hours of Friday to fiercely defend the president and accuse “donors” and “elites” of trying to cast him and vice-president Kamala Harris aside.Biden’s disastrous debate performance against Trump last month sparked panic in the Democratic party over his age and fitness for office. After testing positive for Covid in Nevada he was seen apparently struggling to ascend a staircase into Air Force One to return home.