President Biden on Friday delivered one of the most forceful performances of his campaign, acknowledging that he doesn’t “debate as well as I used to” but firing up a crowd of thousands of supporters by furiously accusing former President Donald J. Trump of being a “one-man crime wave.”

Speaking to a large and boisterous crowd, Mr. Biden, 81, tried to beat back a chorus of doubters that emerged following a devastating debate against Mr. Trump the night before, when he appeared disjointed and unclear.

On Friday, he was once again the fierce and loud-spoken campaigner that many had doubted still existed. He directly confronted questions about his age, saying that “I know I’m not a young man, to state the obvious.”

But he sought to minimize concerns about his own fitness for office, saying he would never run for re-election if he didn’t think he was up to the job. And he repeatedly sought to cast the election as a choice between right and wrong, morality and criminality, an honest man and a convicted criminal.

“I don’t speak as smoothly as I used to,” he said to roars of approval from the crowd in a fairgrounds hanger. “But I know what I do know. I know how to tell the truth. I know right from wrong. And I know how to do this job. I know how to get things done.”