ATLANTA, United States: U.S. President Joe Biden's supporters had hoped Thursday night's debate would erase worries that the 81-year-old was too old to serve another term, but his hoarse voice and at times tentative performance against Republican rival Donald Trump did the opposite.

Biden and Trump, 78, both have faced concerns about their age and fitness in the run-up to the Nov 5 election, but they have weighed more heavily on Biden.

On Thursday, with his voice hoarse from a cold, Biden hurried through some of his talking points on the debate stage, stumbled over some answers and trailed off during others.

About halfway through the debate, a Democratic strategist who worked on Biden's 2020 campaign called it a "disaster."

Trump unleashed a barrage of criticisms including well-worn falsehoods like migrants carrying out a crime wave and that Democrats support infanticide.

Early in the debate, Biden paused as he was making a point about Medicare and tax reform and seemed to lose his train of thought.

Tax reform would create money to help "strengthen our healthcare system, making sure that we're able to make every single solitary person eligible for what I was able to do with the, with the Covid, excuse me, with dealing with everything we had to do with," Biden said, pausing.

"We finally beat Medicare."

Trump jabbed Biden for being incoherent, saying at one point: "I really don't know what he said at the end of that sentence.

"I don't think he knows what he said."

"Biden's not talking in a measured way, and looks like he's searching for words," said Ray La Raja, a political science professor at the University of Massachusetts Amherst.

Ahead of the debate, Biden confined himself to nearly a week of "debate camp" with top advisers at the Camp David presidential retreat in the mountains of western Maryland, an indication of how important his campaign considered Thursday night.

It didn't reflect on his performance, critics said.

"Trump is Trump, every word out of his mouth is bullshit. But Biden sounds old. And lost. And that's going to matter more than anything.

So far, this is an absolute nightmare for Biden," Joe Walsh, a former 2020 Republican presidential candidate who has been critical of Trump, said on X.

  - Reuters