President Joe Biden mixed up the names of Vice President Kamala Harris and his Republican rival Donald Trump on Thursday but insisted he was pushing ahead with his re-election bid even as more of his fellow Democrats urged him to end his campaign.

Biden, 81, touted his decades of experience on the world stage as he argued that he was uniquely qualified to defeat former President Trump, 78, and lead the U.S. for another four-year term.

"The only thing age does is creates a little bit of wisdom if you pay attention," said Biden, who is already the oldest person to ever serve as president.

Since his poor performance against Trump in a presidential debate two weeks ago, Biden has faced growing doubts from donors, supporters and fellow Democrats about his ability to win the Nov. 5 election and keep up with the demands of the job.

He probably did not help his case when he mixed up his vice president and his Republican rival at the outset of the news conference, which lasted nearly an hour.

"Look, I wouldn't have picked Vice President Trump to be vice president if she was not qualified to be president. So start there," Biden said as he responded to a question from Reuters about his confidence in Harris.

The president coughed frequently and occasionally garbled his responses at the outset of the news conference, and towards the end his answers frequently trailed off before he had completed his thoughts. At the same time, he delivered detailed responses on issues such as the Israel-Gaza conflict and the need for western countries to produce more military weaponry to counter Russia and China.

That came a few hours after Biden mistakenly referred to Ukrainian President Volodymyr Zelenskiy as "President Putin" at the NATO summit in Washington, drawing gasps from those in the room.

Biden's campaign has been on the ropes for two weeks, since his poor debate performance against Trump.

At least 16 of the 213 Democrats in the House and one of the Senate's 51 Democrats have appealed publicly to the president to withdraw from the race.

Representative Jim Himes of Connecticut joined that group shortly after the press conference ended.

"We must put forth the strongest candidate possible to confront the threat posed by Trump's promised MAGA authoritarianism," he said. "I no longer believe that is Joe Biden."

Biden overcame a childhood stutter and has frequently mangled names and misspoken throughout his political career.

Biden said his health is in good shape and that he would take another neurological exam to determine his mental acuity if his doctors recommended it.

Reuters