Joe Biden told MSNBC on Friday night that Trump 'doesn't know that many facts' and is 'not that smart'.
The former VP was discussing Tuesday's first presidential debate.
He claimed Trump would resort to personal attacks because 'it's the only thing he knows how to do'.
Biden said that he refused to acknowledge to comments that there may not be a peaceful transfer of power if Trump loses.
He said that Trump was using the claims to distract from the pandemic.
'The American people aren't going to be shut down in this election,' he said.
Joe Biden hit out at President Donald Trump on Friday night calling him a 'liar' and claiming he's 'not that smart' just days before the first presidential debate.
In an interview with MSNBC, Biden claimed that Trump 'doesn't know that many facts' and so will fall back on personal attacks during Tuesday's debate to be hosted by the network.
He also criticized Trump for 'irresponsible, outrageous attacks on voting'.
Biden was speaking from his home in Delaware after arriving back from Washington D.C. having visited the casket of late Supreme Court Justice Ruth Bader Ginsburg.
'The people know the president's a liar,' Biden said.
'My guess is it's going to be a straight attack, it's going to be personal,' he said of the debate.
'It's the only thing he knows how to do. He doesn't know how to debate the facts because he's not that smart. He doesn't know that many facts.
'He doesn't know much about foreign policy. He doesn't know much about domestic policy. He doesn't know much about the detail,' Biden continued.
In another segment of the interview, host Stephanie Ruhle asked Biden what he would do if he wins and Trump fails to agree to peaceful transfer of power.
Earlier on Friday, Trump claimed that the only way he will lose the presidential election in November is if Democrats cheat through mass mail-in ballot measures implemented in light of in-person voting concerns due to the coronavirus pandemic.
'That's the only way we're going to lose, is if there's mischief,' he told a crowd of his supporters.
'And we do want a very friendly transition,' he assured them.
'But we don't want to be cheated and be stupid and say "Oh let's transition". Well we'll go and we'll do a transition and we'll know that there were thousands and thousands of ballots that made a difference through cheating. We're not going to stand for it.'
Biden told Ruhle that 'the American people aren't going to be shut down in this election'.
'They're going to vote. They're going to vote in large numbers and they're just not going to be denied. It's going to be clear from the beginning exactly where this is going.
'This is a typical Trump distraction,' Biden claimed. 'Trying to make everyone wonder whether or not the election will be legit and whether or not absentee ballots matter while he's writing his absentee ballot out, voting from the Oval Office to run in Florida and vote in Florida.
'The people of this country are going to be heard November 3. Every vote in this country will be heard. It will not be stopped and I'm confident despite all the irresponsible, outrageous attacks on voting, we'll have an election in this country like we'll always have had.
'And he'll leave,' Biden concluded.
The former Vice President was pushed further to answer what he would do if Trump refused to leave.
'The power of the Oval Office relies on those with the authority to enforce what he says and he already has six members of his administration who were four-star generals ... who said that this guy's not fit to be president,' Biden said.
'I don't think he's going to get the FBI to follow him to enforce something that's not real. What I'd get concerned about is whether he generates some kind of response in a way that unsettles the society or causes some kind of violence.
'He talks about "by the time the polls close, I was winning but now these votes coming in late",' he added, referencing Trump's criticism of mail-in ballots.
'I don't think it's going to go anywhere I think the American people are on to this guy. I'm not even going to entertain that because I'm not anticipating that happen.'
Biden then accused Trump of using his claims of voter fraud as a distraction.
'The whole notion of him talking about this is to take our eye off the ball, not to talk about what's happening all the people dying of COVID-19, not talking about all the unemployment, not talking about him being unwilling to get the Congress together, to get off the golf course, not in the sand trap and have a meeting in the White House,' Biden said.
'It's always about distraction with him. I think that's what this is about.'
He also sent a message to Russian leader Vladamir Putin about him implementing consequences for election interference if he wins.
'My message for Vladamir Putin is if I'm elected I'm coming because here's the deal, it's a violation of our sovereignty,' he said.
'I've made it clear before and I'm make it clear again, I was part of a transatlantic commission set up for the elections taking place in Europe where the former Secretary General of NATO and I ... we all got together and we met in Europe and we made a commitment of all those standing in an election and we committed that if there was any interference from outside and we knew about it, we'd call it out, we would not accept it.
'We took that pledge, I took that pledge. This president refused to take that pledge. He would like very much to see Vladamir Putin continue down the road he is but I promise you, there will be consequences.
'There will be consequences if I win for this involvement in our sovereignty,' Biden added.
National polls shows Biden remains favorite to win the White House on November 3