Biden defiant on campaign trail but pressure mounts

But as he addressed a lively rally in the battleground state of Michigan, the drumbeat of Democrats urging the 81-year-old Biden to step aside kept getting louder following a disastrous debate performance against Trump.

"There's been a lot of speculation lately. What's Joe Biden going to do, is he going to stay in the race, is he going to drop out?" Biden told supporters in the city of Detroit, to chants of "Don't you quit!"

"Here's my answer: I am running and we're going to win! I'm not going to change that," Biden said.

Opposition continued to grow however despite a defiant Biden coming out fighting at a high-stakes press conference at a NATO summit in Washington on Thursday.

Nineteen Democratic lawmakers have now called on him to bow out of the race due to concerns over his health and mental acuity in the wake of the June 27 debate debacle.

He told his first solo news conference for eight months that he was the "most qualified" person to run for president. It was watched by 24.2 million people in the United States, almost half the number who saw the debate.

'President not a dictator'

A series of gaffes at the summit, including referring to Vice President Kamala Harris as "Vice President Trump" and mixing up Ukrainian President Volodymyr Zelensky with Russian strongman Vladimir Putin, kept the focus on his fitness to serve.

At the Detroit rally Biden tried to brush off the blunders.

In scenes more reminiscent of rallies by his rival where the press are often abused, reporters in Detroit were booed after Biden addressed them and said they were "hammering me because I sometimes confuse names."

Biden then urged the media to focus on Trump's "lies" and on "Project 2025," a blueprint for power by hard-line conservatives that Democrats have said the former president would implement.

The 78-year-old Trump denies he is involved with the program

"Americans want a president not a dictator," Biden said to cheers. Referring to Trump's comment that he would only be a dictator on "day one" of his presidency, Biden said he would let that happen "over my dead body."

Earlier, Biden said "I promise you I am OK" as he addressed supporters at a diner.

Biden, who blamed jet lag and illness for his stumbling debate performance, will keep up a relentless travel schedule in coming days as he seeks to allay concerns over his stamina and sharpness.

"The president understands that there's still some anxiety," Biden campaign communications director Michael Tyler told reporters traveling to Michigan with the president aboard Air Force One.

"That's why he's laser focused on demonstrating that he is the best person to take on Donald Trump," he said.

'Gaffes for 40 years'

Tyler played down the verbal slip-ups, saying: "Joe Biden has been making gaffes for 40 years, he made a couple of last night, he probably will continue to do so."

The top Democrat in the House of Representatives, Hakeem Jeffries, meanwhile said he had met with Biden late Thursday after the press conference.

Jeffries said he "expressed the full breadth of insight, heartfelt perspectives and conclusions about the path forward" but did not give further details.

Next week Biden heads to Texas and Nevada to reach out to his vital Black and Latino voters, and will give his second major network interview of recent weeks on Monday to broadcaster NBC.

The concerns over Biden are affecting Democratic donors, with Hollywood star and high-profile supporter George Clooney calling on Biden to step aside on Wednesday.

A number of other key donors have told the largest Biden campaign fund that around $90 million in pledged donations is on hold if he carries on running, the New York Times reported on Friday.