A halting Joe Biden struggled Thursday to allay concerns he is too old for a second term in the White House in a fiery debate with Donald Trump marked by personal insults.

Biden, who was said to have a cold, hit Trump with clearly rehearsed lines as he sought to remind millions of television viewers that Trump would be the first convicted felon in the White House.

“You have the morals of an alley cat,” Biden said.

Trump, a veteran of rallies and reality television, spoke loudly as he ran through a long list of complaints about Biden’s record.

“I’m friends with a lot of people. They cannot believe what happened to the United States of America. We’re no longer respected,” Trump said.

Trump sought to seize on Biden’s delivery, 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 either.”

Vice President Kamala Harris went into damage-control mode.

In a live interview on CNN, Harris said Biden’s record was “extraordinarily strong” but acknowledged concerns about his debate.

“Yes, there was a slow start, but it was a strong finish,” Harris said.

Kate Bedingfield, a former Biden communications director, said on CNN that “it was a really disappointing” evening for the president.

“I don’t think there is any other way to slice it,” she said.

A CNN poll found 67 percent of debate watchers thought Trump had won the event.

Democrats are set formally to name Biden as their candidate in August in Chicago, with little way to change course unless the president himself withdraws.

Biden has sought to counter attacks by Trump who say he is not vigorous enough for the job.

But Julian Zelizer, a historian at Princeton University, said Biden’s supporters would be “extremely concerned.”

“Biden fueled the basic perception that has continued to overshadow him,” he said.

At a watch party in San Francisco, Hazel Reitz said she would still vote for Biden but added: “I can’t understand a word that he says. Isn’t it sad?”

AFP.