Biden blames international travel for poor debate performance, says he nearly 'fell asleep on stage'.

At a campaign fundraiser in McLean, Virginia, on Tuesday evening, President Joe Biden -- for the first time -- attributed his poor debate performance last week to the amount of foreign travel he did in June, according to notes from a small group of reporters permitted in the event.

"I decided to travel around the world a couple of times," Biden said, referring to recent trips abroad, including his visit to France for the 80th anniversary of D-Day.

"I didn't listen to my staff,” he continued, adding he "came back and nearly fell asleep on stage."

Biden said Tuesday he was sorry for his debate performance but stressed that winning the election was "critical."

"It's not an excuse but an explanation,” he continued, adding that the DNC and Biden campaign have raised millions of dollars since debate night.

"I feel good about it," he said.

Biden's debate performance last Thursday triggered renewed concern over his age and mental acuity among political observers, including some Democrats who have begun to have discussions about his ability to carry on as their party's nominee.

The president first addressed his poor debate performance at a North Carolina rally the day after the debate.

"Folks, I know I'm not a young man, to state the obvious," he told the crowd.

"I don't debate as well as I used to, but I know what I do know. I know how to tell the truth," he said to loud cheers from an enthusiastic campaign crowd.

Last Saturday, he also touched on it at a fundraiser at the home of New Jersey Gov. Phil Murphy.

"I didn't have a great night, but I'm going to be fighting harder," Biden told attendees of the event.

Earlier on Monday evening, the Biden campaign held a call with more than 500 regional and national finance chairs – who raise money for the campaign and the Democratic Party – during which senior campaign advisers defended Biden's health and gave assurances he could carry on with his 2024 campaign.

The campaign advisers also noted that a few hundred campaign events in support of Biden took place around the country this past weekend. They also touted the fundraising haul since the debate, people who were on the call told ABC News, with the campaign and the Democratic Party raking in $33 million.