Democrats are pointing out that Joe Biden was speaking to George Lopez when he said Sunday 'four more years of, George'.
Republicans interpreted Biden's comment as a gaffe and suggested he had forgotten President Donald Trump's name.
They speculated that Biden, known to be gaffe-prone, was speaking about Presidents George W. Bush or the late George H.W. Bush.
Trump used Biden's comment on the campaign trail Monday mocking him for misremembering the president's name at an Allentown, Pennsylvania rally.
'He could not remember my name yesterday, this is what you're putting in office,' Trump told the crowd.
Democrats and other Biden allies are pointing out that Joe Biden was speaking to George Lopez when he said 'four more years of, George' during a virtual concert, as President Donald Trump continued to ridicule him Monday for not remembering the president's name.
'Can you even imagine losing to a guy like this? Actually I wish he was a good and even a great candidate because if something happened you'd feel a little better. But can you imagine? He can't remember my name,' Trump told a crowd of supporters Monday in Allentown, Pennsylvania. 'Now, I'm not that big of an ego guy,' the president joked.
Biden and his wife Jill were participating in a star-studded virtual concert Sunday night when he said, '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.'
While Lopez was on the Zoom call at the time, Republicans quickly interpreted Biden's remarks as the former vice president confusing who was in office - with George referring to either President George W. Bush or President George H.W. Bush, who is dead.
In a Monday morning tweet, Trump wrote, 'Joe Biden called me George yesterday. Couldn't remember my name. Got some help from the anchor to get him through the interview. The Fake News Cartel is working overtime to cover it up!'
Video of his comments showed Jill Biden moving her mouth, with observers suggesting she had prompted Biden with the name 'Trump' to get him back on track.
The moment was seized upon by Trump War Room Twitter account. 'WATCH: Joe Biden confuses President Trump with George Bush,' the account tweeted Saturday.
Even though Trump has his own record of messing up names - such as calling Apple CEO Tim Cook 'Tim Apple' or screwing up Rep. Matt Gaetz's name at a recent rally - the president still used it as an attack line at his first rally Monday.
'I'm the candidate and I happen to be president,' Trump pointed out. 'He could not remember my name yesterday, this is what you're putting in office.'
'I don't think he's going to make it, I don't think he's going to make it,' Trump continued.
At the same rally, Trump mixed up the World Health Organization and the World Trade Organization.
The president falsely said that Biden had called a 'lid' for the day - parlance journalists use to say a candidate isn't leaving the house.
In fact Biden did leave his Delaware home, making a trip - like Trump - to Pennsylvania for some Q&A in Chester.
'Ladies and gentleman, the Vice President Biden will be doing a lid today. I hear he's doing a lid until Thursday,' Trump claimed. 'Hey media, is it until Thursday he's doing a lid? Thursday!' the president yelled to the reporters near the back of his rally crowd.
Biden has plans to travel to Georgia, typically a bright red Republican state, on Tuesday, following in the footsteps of his running mate Sen. Kamala Harris who made stops in Atlanta on Friday.
For months, Biden's campaign has said it is focusing on re-establishing the Democratic 'blue wall' in Wisconsin, Michigan and Pennsylvania that crumbled when all three went for 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.
On Monday, his campaign also announced stops in Wisconsin and Iowa, two states Trump won in 2016.
Both his Georgia and Iowa stops indicate he sees the Trump administration's 'reckless' federal response to the coronavirus pandemic as a chance to gain ground.
On Sunday, Biden and his wife campaigned virtually, appearing during the star-studded 'I Will Vote Concert' which was headlined by A$AP Ferg, Sara Bareilles, Aloe Blacc, the Black Eyed Peas, Jon Bon Jovi and Cher.
It garnered around 12,000 views and was live-streamed on YouTube.
It comes just two days after the former vice president said during an interview: 'We have put together, I think, the most extensive and inclusive voter fraud organization in the history of American politics.'
Biden was speaking about his campaign's moves to combat voter suppression.
This, too, was seized upon by Trump's team, with White House press secretary Kayleigh McEnany tweeting from her personal account: '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,' Biden continued.
'I'm happy to have that comparison,' the former vice president added.
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.
Trump 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.'
August 8, 2019: He tells the Asian & Latino Coalition in Des Moines, Iowa, that 'poor kids are just as bright and just as talented as white kids.'
He attempted to clear up his statement, adding: 'Wealthy kids, black kids, Asian kids — no, I really mean it. But think how we think about it ... mWe think how we're going to dumb it down. They can do anything anybody else can do given a shot.'
Later that day he tells a crowd: 'We choose unity over division. We choose science over fiction. We choose truth over facts.'
August 9: Biden was accosted by a right-wing Turning Point USA staffer at a rally in Iowa. 'How many genders are there?' He asked.
Biden replied: 'There are at least three.'
The reporter said, 'What are they?'
And Biden responded: 'Don't play games with me, kid.' Biden then shook someone in the crowd's hand before turning back and saying, 'By the way, the first one to come out for marriage was me.'
August 10: Biden says he was VP when the Parkland school shooting took place, even though it occurred in 2018.
'Those kids in Parkland came up to see me when I was vice president,' he told a reporter.
A campaign official clarified that Biden meant the shooting at Sandy Hook Elementary School in Connecticut, in December 2012.
August 24: Biden mistakes New Hampshire for Vermont.
Speaking in Keene, NH, he said: 'I love this place. Look, what's not to like about Vermont in terms of the beauty of it?'
September 2: Biden appears confused about the definition of a magazine for a rifle, telling supporters in Iowa: 'The idea that we don't have elimination of assault type weapons, magazines that can hold multiple bullets in them, it's absolutely mindless.'
By definition a magazine holds multiple rounds.
September 25: Biden forgot the name of the last Supreme Court nominee under President Barack Obama on Jimmy Kimmel's show.
'Back when, when they were holding up before Trump got elected, they were holding up, uh, um, the nomination of the president put forward for the Supreme Court,' Biden rambled.
'Merrick Garland,' Kimmel said.
'Merrick Garland, a really fine man,' Biden added.
November 2: Says he's in Ohio when he's in Iowa.
November 20: Biden claimed that he had the backing of the Senate's only black female Senator during a Democratic debate.
'I have more people supporting me in the black community that have vouched for me because they know who I am… The only African-American woman who's ever been elected to the United States Senate.'
Senator Kamala Harris corrected him, saying: 'That's not true. The other one is here!'
December 5: He called a voter a 'damn liar' and 'fat' after he asked if his son Hunter earned a job on the board of a Ukrainian gas company as a result of his father's high office.
'You're a damn liar, and that's not true,' Biden snapped at him. 'I'm not sedentary. You want to check my shape, let's do push ups together, let's run, let's do whatever you want to do, let's take an IQ test.'
He continued, 'But look, fat, here's the deal.'
February 9, 2020: Biden called a 21-year-old woman a 'lying, dog-faced pony soldier' during a Q&A in New Hampshire.
Asked by the economics student Madison Moore about his poor performances in the Iowa caucuses, he asked if she'd ever attended a caucus. Moore said she had and Biden hit back: 'No you haven’t! You’re a lying, dog-faced pony soldier.'
February 24: 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 1: He calls Fox News host Chris Wallace 'Chuck,' and then claims it was because he'd had a recent interview with NBC's Chuck Todd.
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 3: He confused his wife with his sister on stage at a rally in California.
'By the way, this is my little sister Valerie!' Biden said while grabbing his wife's right hand. 'And I'm Jill's husband,' he went on while reaching for his sister's.
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.'
April: He appeared to forget Barack Obama's name while discussing Russia's annexation of Crimea.
'Because they invaded another country and annexed a significant portion of it called Crimea. He's saying that it was president - my boss - it was his fault.'
May 22: Biden tells radio host Charlmagne the God that 'if you have a problem figuring out whether you're for me or Trump, then you ain't black.'
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 15: Biden says that wealthy people were able to stay home during lockdown because 'some black woman was able to stack the grocery shelf.'
Speaking to a group of veterans in Tampa, Florida, he said: 'The American public, the blinders have been taken off. They've all of a sudden seen a hell of a lot clearer.
'They're saying: "Jeez, the reason I was able to stay sequestered in my home is because some black woman was able to stack the grocery shelf."'
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.'
October 24: He tells a virtual meeting: 'We have put together, I think, the most extensive and inclusive voter fraud organization in the history of American politics.'
October 25: He got confused about who is president, calling him, 'George.'
Speaking at the 'I Will Vote Concert' Biden said: '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.'
He was aided by his wife Jill who appeared to mutter 'Trump,' under her breath while Biden struggled for the words.