All week, Biden has refused to answer when questioned if he would increase the size of the high court to gain a liberal majority if Democrats gain the White House and Senate in November.
'What that means, really, is that they're going to do it, because obviously, that means 100 percent that's what they're going to do,' Trump said.
'They're going to end the filibuster and they're going to do things that you wouldn't have thought,' Trump continued.
'If they ever got in, day one, this would be the first move they make, end the filibuster -- the nuclear option, as they call it -- and they will do that,' the president stated. 'Not a week will go by, probably not a day will go by.'
At a campaign event earlier the same day, Biden kept dodging the question whether he'd support raising the number of justices on the Supreme Court.
This move is referred to as 'court-packing' - that some liberals have pitched to balance the conservative tilt of the court under President Donald Trump, particularly with his new choice of Judge Amy Coney Barrett to replace the late Justice Ruth Bader Ginsburg.
'They'll know my opinion on court-packing when the election is over,' Biden told.
The statement drew angry comments, as Kayleigh McEnany of the Trump campaign tweeted: “Voters deserve a clear answer, though we basically already have one. Joe Biden WILL pack the Supreme Court!” in response.
Biden's running mate, Sen. Kamala Harris also dodged the question during her debate Wednesday night against Vice President Mike Pence.
She was repeatedly asked to answer it by Pence, though she changed the subject repeatedly.
'Let's talk about packing the court,' she told Pence.
Of the 50 people who president Trump appointed to the Court of Appeals, not one is black. You want to talk about packing a court? Let's have that discussion,' Harris continued.
Biden also answered dodging his means when he was previously asked the question.
'I don't blame you for asking it, but you know the moment I answer that question, the headline in every one of your papers will be about that, other than - other than focusing on what's happening now,' Biden said Thursday.
Conservative activists have been infuriated by Biden's continued unwillingness to answer.
'Today Joe Biden insulted voters by wimping out on the court-packing question, all but admitting that he would radically change one of the three branches of government without having the guts to actually say so,' tweeted Judicial Crisis Network President Carrie Severino Thursday afternoon.