WASHINGTON, July 3, 2024 (BSS/AFP) - Democrats shocked by Joe Biden's dismal debate performance urged the US president Tuesday to be transparent about his mental fitness as he faced the first call from his own side to drop out of the election.

Some supporters have expressed growing doubts about the 81-year-old's candidacy after last week's televised showdown with Donald Trump, when Biden stumbled over his words and lost his train of thought -- exacerbating fears about his age.

Congressman Lloyd Doggett became the first Democratic lawmaker to publicly call on Biden to make way for another candidate, saying he was hopeful the president would "make the painful and difficult decision to withdraw."

Nancy Pelosi, a Democratic Party heavyweight and former speaker of the House, said it was "legitimate" to ask whether Biden's debate disaster was indicative of a deeper problem rather than a one-off.

Biden has not given a live interview since the debacle, but will be interviewed by ABC on Friday with the first clips released later that day.

On Tuesday, he blamed exhaustion from international travel for his debate flop.

Speaking at a fundraiser, Biden said he "wasn't very smart" for "traveling around the world a couple times... shortly before the debate."

"I didn't listen to my staff," he said. "And then I almost fell asleep on stage."

- 'Horrified' -

Biden traveled to France from June 5 to 9 to commemorate the 1944 Allied landings, headed back to the United States, and then flew to Italy for a G7 summit followed immediately by a visit to California.

He then returned home and went to a presidential retreat for several days of rest and preparation for the debate.

White House press secretary Karine Jean-Pierre on Tuesday admitted the debate was "a bad night" but added that Biden "knows how to come back" from adversity.

She dismissed questions about him needing a cognitive test, and said the president would hold a press conference during a NATO summit in Washington next week.

The polling margins between the president and his Republican predecessor have been razor-thin for months, with Trump showing a slight advantage.

Biden pushed for an unusually early first debate in hopes that he could jolt the race while there was still time -- but the plan backfired.

Democratic Senator Sheldon Whitehouse told WPRI-TV he was "pretty horrified" by the president's performance during the 90-minute CNN match-up, watched by more than 50 million Americans.

Jared Golden, a vulnerable Democrat in a conservative-leaning House district, raised eyebrows with an op-ed in his local paper in Maine in which he said Biden's poor showing "was not a surprise."

"The outcome of this election has been clear to me for months: While I don't plan to vote for him, Donald Trump is going to win," he wrote.

The White House said Biden would meet with Democratic governors on Wednesday evening.

One of them, J.B. Pritzker of Illinois, explained that the governors had asked for the opportunity to hear from the president directly.

"Right now, Joe Biden is our nominee, and I'm 100 percent on board with supporting him as our nominee, unless he makes some other decision, and then I think we're all going to be discussing what's the best way forward," he told CNN.

- Slowing down -

Biden has visibly slowed over the last year.

It has been several months since the president, who has tripped or fallen in public on several occasions, stopped using his plane's high gangway, preferring a shorter, more stable staircase.

He has also surrounded himself with aides for the short walk from the White House to his helicopter on the lawn, hoping to prevent cameras from focusing on his stiff gait.

Biden, who has always been gaffe-prone, has not given a long press conference since January 2022 and spends most weekends in one of his Delaware homes, with no official schedule.

Vice President Kamala Harris -- a leading contender to replace Biden if he exits the race -- said Tuesday she was proud to be his running mate.

"We beat Trump once and we're going to beat him again," she said.