Former President Trump on Sunday lambasted his former Attorney General William Barr after Barr described Trump's repeated unsubstantiated claims about the 2020 election as "bullshit" in a forthcoming book.

"Bill Barr was a disappointment in every sense of the word," Trump said in a statement issued late Sunday. "Besides which, Barr, who was Attorney General (lawyer) shouldn't be speaking about the President."

"Instead of doing his job, he did the opposite and told people within the Justice Department not to investigate the election," Trump continued. "Just like he did with the Mueller report and the cover up of Crooked Hillary and RUSSIA RUSSIA RUSSIA, they don’t want to investigate the real facts. Bill Barr’s weakness helped facilitate the cover up of the Crime of the Century, the Rigged 2020 Presidential Election!"

The statement from Trump is the latest episode in the months-long falling out between the former president and Barr, who spent nearly two years as attorney general under Trump.

In a newly published excerpt from ABC News correspondent Jonathan Karl's upcoming book, "Betrayal," Barr described the rapidly deteriorating relationship he had with Trump as the then-president became more entrenched in his belief that the 2020 election was fraudulent.

“If there was evidence of fraud, I had no motive to suppress it. But my suspicion all the way along was that there was nothing there. It was all bullshit,” Barr told Karl.

Barr also told Karl that Senate Minority Leader Mitch McConnell (R-Ky.) had urged the then-attorney general to push back against Trump's falsehoods, worrying that Trump's rhetoric would cost the GOP in January's Senate runoff elections in Georgia. Democrats went on to win both races and control of the chamber as a result.

Trump, in a lengthy statement on Sunday, decried Barr as a "RINO" — Republican in name only — who "really let down the American people." He complained about Barr's handling of the 2020 election and bemoaned that his former attorney general did not sufficiently investigate wrongdoing during the Obama administration. Trump in the final days of the 2020 campaign had pushed Barr to investigate President Biden's son Hunter Biden. 

"Now it was revealed that Barr was being pushed to tell lies about the election by Mitch McConnell, another beauty, who was worried about damaging the Republicans chances in the Georgia runoff," Trump said. "What really damaged the Senate Republicans was allowing their races to be rigged and stolen, and worse, the American people to no longer believe their vote matters because spineless RINOs like Bill Barr and Mitch McConnell did nothing."

Trump has for months spread the false conspiracy theory that the 2020 election was rigged against him, pointing to what he calls suspicious votes in Georgia, Arizona, Pennsylvania and elsewhere. But GOP state officials in those states have concluded there was no fraudulent activity that affected the outcome of the election, and numerous judges have dismissed lawsuits brought by the president's allies over the outcome.

The president pointed to Barr's own words in his resignation letter, in which the former attorney general said he was "greatly honored" to have served in the Trump administration. Barr went on to praise Trump at the time, highlighting "the many successes and unprecedented achievements you have delivered for the American people. Your record is all the more historic because you accomplished it in the face of relentless implacable resistance.”

Barr long faced criticism from Democrats, who said he served as Trump's personal attorney and defended the former president rather than the interests of the American public. The former attorney general had agreed there were fraud concerns surrounding mail-in voting leading up to the 2020 election, and it was not until weeks after Election Day that he told The Associated Press there was no evidence of widespread fraud.