Joe Biden said he was “doing 9/11” in a gaffe before the anniversary of the 2001 terror attacks.
Mr Biden, who stood aside as the Democratic Party US presidential candidate in July, made the remarks when asked about a TV debate between Kamala Harris and Donald Trump.
The US President, who decided not to seek another term amid widespread concern about his age, told reporters ahead of the debate on Tuesday: “I’m going up to my granddaughter’s birthday in New York.
“Then we’re gonna watch the debate, then tomorrow I’m doing 9/11.”
Seemingly unaware of the gaffe, which he made while heading to his helicopter on the White House lawn, the 81-year-old added: “I spoke with the vice president. She’s calm, cool, and collected.
“I think she’s going to do great, and I’m not going to tell you what advice I gave her.”
The “doing 9/11” appears to be a reference to his visits to the sites of the attacks on Wednesday.
The remarks were criticised by the Republicans, RNC Research, an X account managed by the Republican National Committee, posting: “YIKES”.
Another X account affiliated to the Republican Donald Trump’s campaign, Trump’s War Room, added: “This is the humiliating cognitive decline Kamala Harris COVERED UP.”
President Biden, former President Donald Trump and Vice President Kamala Harris stood together on Wednesday at ground zero in New York.
Trump and running mate JD Vance arrived at the trade center site around 8 am. and Harris with Biden about a half-hour later.
Cheers of "Donald!" and "Kamala!" sprang from some in the audience.
Biden and Trump shook hands, and former New York Mayor Michael Bloomberg appeared to facilitate a handshake between Harris and Trump. Then the presidential rivals stood only a few feet apart, with Biden and Bloomberg between them, as the observance began with the tolling of a bell and a moment of silence.
Speaking to reporters on-board Air Force One, White House spokesperson Karine Jean-Pierre said earlier: “We can only imagine the heartbreak and the pain that the 9/11 families and survivors have felt every day for the past 23 years and we will always remember and honour those who were stolen from us way too soon.”
It comes as Ms Harris is seen as having won the TV debate against her Republican rival for the November 5 vote, with one instant poll for CNN saying 63 percent of viewers scored a win for the vice president, compared to 37 percent for Trump.
