President Joe Biden has insisted “I am running and we’re going to win” during a boisterous performance at a rally in Detroit.
The 81-year-old is trying to shift the conversation from his mental sharpness after a shaky debate performance and two high-profile gaffes at the NATO summit.
“I’m the nominee,” he said. “I’m not going anywhere.
“It’s time for us to stop treating politics like it’s entertainment or a reality TV show.”
And to wild cheers, he shouted: “Donald Trump is a loser!”
Mr Biden also warned Project 2025, a conservative policy platform that would seek to slash the federal government if Donald Trump is elected, was “deadly serious”.
Mr Biden also got a boost earlier in the day when two prominent Democrats – Representative James Clyburn and California Governor Gavin Newsom – said he should stay in the race.
But there have been signs that his support was weakening elsewhere, as two more lawmakers called on him to drop out.
“It is time to move forward. With a new leader,” Representative Mike Levin, from California, said in a statement.
Since the debate, at least 19 lawmakers have urged Mr Biden to step aside so the party can pick another candidate, as have some donors, Hollywood stars, activist groups and news outlets.
The president retains support from key figures in the party, however.
“I’m riding with Biden no matter which direction he goes,” Mr Clyburn said on NBC’s Today programme.
While Mr Biden courted Michigan voters, Trump challenged him on Friday to take a cognitive test.
“I will go with him and take one also. For the first time we’ll be a team, and do it for the good of the Country,” he said on Truth Social.
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As well as the debate disaster, Thursday’s closely-watched news conference provided ammunition for Mr Biden’s supporters and doubters alike.
At one point, he referred to his vice president, Kamala Harris, as “Vice President Trump”.
Hours earlier he introduced Ukrainian President Volodymyr Zelenskyy as “President Putin” at the NATO summit, drawing gasps from those in the room.
However, he also delivered detailed assessments of global issues that served as a reminder of his decades of experience on the world stage.
An NPR/PBS poll released on Friday found Mr Biden leading Trump 50% to 48%, a slight increase from his position before the 27 June debate.
But some analysts have warned he is losing ground in the handful of competitive states that will determine the outcome of the election.