WASHINGTON (AP) — President Joe Biden has offered plenty of excuses for his terrible performance in last week's presidential debate. None of them have done much to assuage Democrats' concerns about Donald Trump returning to the White House.

For its part, Biden's White House insists these are explanations, not excuses. But they have only intensified the concerns Democrats have about their presumptive nominee's readiness.

A bad cold

In the initial moments of Thursday's debate, shortly after the 81-year old Biden claimed to a baffled audience that "we finally beat Medicare," aides said the president was suffering from a cold.

Biden's voice was raspy. His eyes looked glassy at times. But despite the cold, he went from the debate to a watch party and then a Waffle House. Then he gave an energized speech Friday in North Carolina.

White House press secretary Karine Jean-Pierre said at Wednesday's news briefing that she initially leaned into the cold as an explanation, but she knew his schedule and jet lag were issues. She later suggested that Biden traveled and then got a cold, possibly linking the two.

"That was my bad," Jean-Pierre said of not discussing jet lag earlier.

Studied too hard

Other aides said Biden had simply overprepared during his time at the Camp David presidential retreat — that the president had simply crammed too many facts in his head.

Biden spent six full days in Maryland at Camp David, which is located in Catoctin Mountain Park. Jean-Pierre said Biden also performed all his presidential duties while working late.

Not feeling great

Biden's wife, Jill, told supporters Friday in New York City that he didn't "feel that great" during the debate. It's not clear what that meant, whether it was the cold, a sense of exhaustion or something else. But the first lady put forward the campaign's main argument that 90 minutes should not define his entire presidency.

Jet lag — from a trip nearly two weeks earlier

Biden offered another explanation Tuesday night at a Virginia fundraiser, saying his problem was jet lag after having gone to France, California and then Italy before taking down time in Delaware and at Camp David. He arrived at Camp David on June 20, seven days before the debate. The presidential retreat is in the Eastern Time Zone, the same as CNN's studios in Atlanta.

"I decided to travel around the world a couple of times, going through I don't know how many time zones," said Biden, adding that he went through "15 time zones" and joking that he "then came back and nearly fell asleep on stage."

That explanation raised more questions about how long Biden requires to recover from travel.

"I would say I don't think it's a new excuse," Jean-Pierre said of the jet lag, adding that it was a lot of travel before stressing that "we certainly don't want to explain this away."

Why he didn't do more damage control: Air travel

Jean-Pierre later added that Biden did not do more damage control on his debate performance immediately afterward because he was traveling in North Carolina, New York and New Jersey before returning late Saturday night to Camp David.

Air Force One is equipped with extensive communications equipment so that presidents can stay informed while midair.