US President Joe Biden is facing a wave of doubts following his televised showdown with Republican rival Donald Trump
US President Joe Biden is facing a wave of doubts following his televised showdown with Republican rival Donald Trump 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 following last week's televised showdown with Donald Trump, after 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.

"Recognizing that, unlike Trump, President Biden's first commitment has always been to our country, not himself, I am hopeful that he will make the painful and difficult decision to withdraw. I respectfully call on him to do so," the Texan said in a statement.

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

She praised Biden's vision and "strategic thinking" in an interview with cable network MSNBC -- but admitted he had had a "bad night" and said it was fair to raise the mental acuity of "both candidates."

Democratic Senator Sheldon Whitehouse also asked for reassurances, saying voters needed to know there would be no repeat of Biden's sub-par showing.

Whitehouse, of Rhode Island, 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.

Biden has not given a live interview or held a press conference since the debacle, meaning he has not had to give unscripted comments under pressure again.

On Monday, at the end of a brief speech about a Supreme Court decision, a journalist asked him if he planned to withdraw from the race for the White House. Biden left the room without answering.

The polling margins between the president and his Republican predecessor have been razor-thin and almost static for months, with Trump showing a slight advantage in the all-important swing states.

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

The White House has always dismissed questions about Biden's mental acuity, sometimes with marked irritation.

His campaign -- under pressure over its tactics -- hit out at "self-important podcasters" in a memo widely seen as a swipe at a group of former Barack Obama staffers and slammed demands from "the bedwetting brigade" for Biden drop out.

"I really do criticize the campaign for a dismissive attitude towards people who are raising questions for discussion," Vermont Senator Peter Welch, a Democrat, told news website Semafor on Tuesday.

Observers say Biden has visibly slowed over the last year.

It has been several months since the president, who has fallen in public on several occasions, stopped using his plane's wide 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, preventing cameras from focusing on his slow, deliberate walk.

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

When he recently visited France to commemorate the 1944 Allied landings, he went straight from the airport to his hotel, where he remained locked up for an entire day, with no public appearances.