US President Joe Biden, scrambling to defuse a political crisis over his shaky debate performance, mocked and criticised Donald Trump at a rally in a spirited speech meant to mute calls for him to quit the race because of his age. 

Biden travelled to Wisconsin, a political battleground state, to rally voters and sit for a television interview that will be closely watched after his debate with Trump prompted some Democrats and donors to question whether he can handle a second four-year term. 

“We had a little debate last week. Can’t say it was my best performance. But ever since then there’s been a lot of speculation. ‘What’s Joe gonna do? Is he gonna stay in the race? Is he gonna drop out?” Biden said. “Well here’s my answer: I am running and gonna win again.” 

Biden said he was thankful for the support of his vice president, Kamala Harris, who has emerged as a top choice to replace him were he to step aside as the Democratic Party’s standard-bearer. 

Biden knocked Trump’s intelligence and called him a liar, delivering stinging attacks that were absent when he appeared on the Atlanta debate stage. 

While in Wisconsin, Biden will be interviewed by ABC News, part of a flurry of events over the next week aimed at showing Americans he still has the stamina to run against Trump in the November 5 election. 

Biden is under pressure from some Democrats to step aside and open a path for the 59-year-old Harris to lead from the top of the ticket. 

A handful of donors and business leaders are making their displeasure known loudly, halting funding or looking at possible Democratic alternatives. Even some of Biden’s closest political allies, including former Speaker Nancy Pelosi, have raised questions about his health. 

Massachusetts Governor Maura Healey issued a statement on Friday in which she asked Biden to weigh the decision carefully, the rare Democratic governor not to issue a statement of support in recent days. 

“President Biden saved our democracy in 2020 and has done an outstanding job over the last four years,” she said. “The best way forward right now is a decision for the president to make. Over the coming days, I urge him to listen to the American people and carefully evaluate whether he remains our best hope to defeat Donald Trump.” 

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Some public opinion polls have shown Trump widening a lead since the debate, while a Reuters/Ipsos poll found one in three Democrats want Biden to quit the race. 

A group of business and civic leaders urged Biden to end his reelection bid in a letter to the White House on Friday, a day after its CEO said members would still back him if he continued to run, the Washington Post reported. 

The White House has blamed a cold for Biden’s shaky performance and Biden himself cited jet lag from back-to-back trips to Europe. 

The ABC interview offers the likelihood of unscripted comments from Biden, who relies heavily on the use of a teleprompter for his public remarks. 

Biden’s former chief of staff, Ron Klain, who led his preparation process ahead of the debate, pushed back against donors complaints. “We are the Democratic Party!” he wrote on X. Donors “don’t get to decide to oust a pro-labor pro-people President”. 

Trump’s campaign and some of his allies have launched a pre-emptive political strike on Harris, moving swiftly to try to discredit her amid talk that she could eventually replace Biden as the Democrats’ nominee. 

The Biden campaign has shown no signs of changing course, although the Trump team has overtaken it on fundraising. 

The campaign announced it would spend US$50 million ($81m) on a media blitz for July, “including strategic investments around key events that draw in large and politically diverse audiences like the 2024 Olympic Games and the Republican National Convention.” 

Trump, 78, who made multiple false statements during the debate in Atlanta, falsely claimed in a video that was circulated on social media that he had driven Biden out of the race. He made disparaging comments about Harris in the same video, which the Trump campaign stood by.