Donald Trump’s attorney general, William Barr, thought Trump might have refused to leave office at all had the Department of Justice not immediately investigated and disproved his lies about electoral fraud in his defeat by Joe Biden.

“I am not sure we would’ve had a transition at all,” Barr said, in startling video testimony played by the January 6 committee on Thursday.

The hearing, the fifth in a series set to extend into July, focused on Trump’s attempts to pressure the justice department to aid his attempt to overturn the election result – an attempt which culminated in the deadly attack on the US Capitol on 6 January 2021.

In December 2020, Barr publicly rejected Trump’s claim of widespread fraud in the November election, and resigned.

He was replaced, as acting attorney general, by Jeffrey Rosen. Rosen testified on Thursday alongside his deputy, Richard Donoghue, and Steven Engel, who led the DoJ Office of Legal Counsel.

Questioning led by Adam Kinzinger of Illinois, one of two Republicans on the committee, focused on Trump’s pressure on the witnesses to go along with his increasingly outlandish claims of widespread fraud.

Before that, the deputy committee chair, the Wyoming Republican Liz Cheney, introduced Barr’s remarks.

She said: “Millions of Americans have seen the testimony of Attorney General Barr before this committee. At one point in his deposition, [Barr] was asked why he authorised the Department of Justice to investigate fraud in the 2020 election.”

Barr, Cheney said, was “asked why not just follow the regular course of action and let the investigations occur much later in time, after 6 January”, the day electoral college results were certified at the Capitol.

Barr said: “I felt the responsible thing to do was to be in a position to have a view as to whether or not there was fraud. Frankly, the fact I put myself into the position that I could say we had looked at this and didn’t think there was fraud was really important to moving things forward.

“I shudder to think what the situation would have been, if the position of the department was, ‘We’re not looking at this until after Biden is in office.’

“I am not sure we would’ve had a transition at all.”

In a previous hearing Barr was shown to have described Trump’s claims about electoral fraud as “bullshit”.

He has also said he will still vote for Trump if Trump runs for the White House again.