Joe Biden last night seemed to forget who the president was, noting that he was fighting against 'four more years of George.'
Addressing supporters online, during a virtual concert to drum up enthusiasm, the 77-year-old sat next to his wife Jill.
'Four more years of George, er, George, er, he - we're going to find ourselves in a position where, if Trump gets elected, we're going to be in a different world,' said Biden.
Jill appeared to remind him, under her breath: 'Trump,' as Biden faltered over such an elementary fact that it is the classic question asked of confused patients: 'Who's the President?'
Many speculated that he was thinking of George W. Bush, president from 2001-09, but he may also have been thinking of Bush Senior who was in office from 1989-93.
The blunder will once again raise questions about the 77-year-old's mental capacity - a topic President Trump has repeatedly referenced in the run-up to the election.
The moment was seized upon by Trump War Room, a pro-Trump group which claims to 'punch back 10x harder'.
On social media, people were dismayed.
'Watch his wife saying Trump under her breath 3 times,' said one.
Another remarked: 'The look on Jill's face was like 'come on Joe, get the train back on the tracks...''
It comes just two days after the former Vice President said during a campaign video: 'We have put together, I think, the most extensive and inclusive voter fraud organization in the history of American politics.'
This too was seized upon by the Trump campaign, White House Press Secretary Kayleigh McEnany who tweeted: 'BIDEN ADMITS TO VOTER FRAUD!'
Earlier on Sunday, Biden, in an interview with 60 Minutes, laughed off Trump's attacks on his mental agility.
'Hey, the same guy who thought that the 911 attack was a 7-Eleven attack?' Biden responded.
'He's talking about dementia?
'All I can say to the American people is watch me, is see what I've done, is see what I'm going to do. Look at me. Compare our physical and mental acuity.
'I'm happy to have that comparison.'
He insisted it was Trump - not him - who was losing his grip on reality.
'The way he's handling COVID is just absolutely totally irresponsible,' said Biden.
'He's telling people that we've turned the bend, in one of his recent rallies. Well, he's gone - as my grandpop would say he's gone round the bend. I mean, we are in real trouble.'
However, Biden was unable to walk away from the interview without mangling his data on public schools.
'I can send every single qualified person to a four-year college in their state for $150 billion,' he said.
CBS later said that Biden's advisers later told them he misspoke, and meant to say double that.
The Trump campaign has in recent months turned up the heat on its claim that Biden's mental capacity is fading.
At rallies the president has repeatedly stated that Biden is 'gonzo.'
'He's gonzo folks. He's gone. He has no idea, and the people that are running that party are radical far-left maniacs.' Trump told a rally in Arizona earlier this month.
The President has joked about Biden ending up in a care home during his tenure and the office being taken over by his running-mate Kamala Harris.
A campaign advert in August asked: 'Did something happen to Joe Biden?'
Biden, who would be the oldest ever president, has denied the accusations against him saying that he is 'constantly tested.'
In June he said: 'Look, all you gotta do is watch me, and I can hardly wait to compare my cognitive capability to the cognitive capability of the man I'm running against.'
During Biden's 60 Minutes interview, he was able to laugh off the 'dementia' jibe as well as lash Trump's personal lawyer Rudy Giuliani for his 'smear campaign' against his son Hunter.
Biden spoke out about the laptop scandal and the emails that have been found detailing plans for business ventures involving China and Ukraine.
Biden said he believed that Giuliani, who has touted the laptop around various media outlets seeking publicity, was being used by Russia.
'From what I've read and know the intelligence community warned the president that Giuliani was being fed disinformation from the Russians,' Biden said.
'And we also know that Putin is trying very hard to spread disinformation about Joe Biden. And so when you put the combination of Russia, Giuliani, the president, together - it's just what it is.
'It's a smear campaign because he has nothing he wants to talk about. What is he running on? What is he running on?'
The former VP also spoke with unusual clarity about whether he would change the makeup of the Supreme Court, in the light of Amy Coney Barrett's expected nomination and the conservative bent the court will take.
Biden, who was strongly criticized by his opponents for saying that voters would have to wait until after the election to see his plans for the Supreme Court, said in Sunday's episode that he would convene a panel of Democrats, Republicans and legal scholars to explore all the options.
Biden's running mate, Kamala Harris said that she believed Trump was racist, and that his attacks on her were 'predictable, sadly.'
Harris said that she hoped her role, if elected, will inspire future generations.
She also denied that she disagreed with Biden on healthcare policy and the Green New Deal, insisting that his platform was her platform.
'I would not have joined the ticket if I didn't support what Joe was proposing,' she said.
Biden, who Trump accused of going into hiding last week, is travelling to Georgia this week to make a late stand in a state that hasn't gone blue since 1992.
Biden's campaign says he will be in Warm Springs, Georgia, on Tuesday, the first time he's visited the state since clinching the Democratic presidential nomination.
Senator Harris, made several stops across Atlanta on Friday.
Biden's campaign has for months said it is focusing on re-establishing the Democratic 'blue wall' in Wisconsin, Michigan and Pennsylvania that crumbled when all three went for President Donald Trump in 2016.
But Biden's top advisers have been equally bullish about 'expanding the electoral map' to traditionally Republican states like Arizona and Georgia.
Biden visited Arizona earlier this month. His Georgia swing just one week before Election Day indicates he sees what he calls the Trump administration's bungled federal response to the coronavirus pandemic as a chance to gain more ground.
Biden's best blunders: Claiming 200 million Americans have been wiped out by Covid and forgetting the Declaration of Independence
February 24, 2020: In South Carolina he said: 'My name's Joe Biden. I'm a Democratic candidate for the United States Senate.'
During the same speech he claimed to to have worked with Chinese leader 'Deng Xiaoping' on the Paris Climate Accord - Deng died in 1997.
February 25: During the final Democratic debate he claimed that '150 million people have been killed since 2007' by guns. If that were the case, half the American population would be dead.
March 3: He confused Super Tuesday with 'Super Thursday.'
And during the same speech he botched the Declaration of Independence, saying: 'We hold these truths to be self-evident. All men and women are created, by the, you know, you know the thing.'
March 9: 'Together, I think we can win back the House,' Biden said before correcting himself. 'We're gonna keep the House, increase it and flip the Senate.'
March 10: Biden pledged to ban the 'AR-14,' (instead of AR-15) when challenged by a worker who accused him of 'trying to diminish our second amendment right and take away our guns.'
August 31: Speaking at a steel factory in Pittsburgh, he stumbled badly over his words, saying: 'COVID has taken this year, just since the outbreak, has taken more than 100 years. Look, here’s, the lives, it’s just, it’s uh, I mean think about it. More lives this year than any other year for the past 100 years.'
September 20: Biden said that 200 million had died of coronavirus, confusing a million for a thousand.
'It's estimated that 200 million people have died probably by the time I finish this talk,' he said.
September 21: He botches the pledge of allegiance, saying: 'I pledge allegiance to the United States of America, one nation, indivisible, under God, for real.'
The correct text is: 'I pledge allegiance to the Flag of the United States of America, and to the Republic for which it stands, one Nation under God, indivisible, with liberty and justice for all.'
October 12: He appeared to forget that he ran against Mitt Romney in 2012.
'You may remember,' Biden said when telling reporters he was opposed to Democrats criticizing Amy Coney Barrett's faith, 'I got in trouble when we were running against that senator who was a Mormon, the governor.'