Donald Trump angrily threatened to leave the Republican Party and start his own political party on his last day as president.

The twice-impeached one-term president told Republican National Committee chairwoman Ronna McDaniel he would start his own party but backed down when GOP leaders threatened actions that would have cost him millions of dollars, according to a book, "Betrayal," written by ABC News correspondent Jonathan Karl.

"[RNC Chairwoman Ronna McDaniel] called to wish him farewell," Karl writes. "It was a very un-pleasant conversation."

"Donald Trump was in no mood for small talk or nostalgic goodbyes," Karl adds. "He got right to the point. He told her he was leaving the Republican Party and would be creating his own political party. The president's son, Donald Trump Jr., was also on the phone. The younger Trump had been relentlessly denigrating the RNC for being insufficiently loyal to Trump. In fact, at the January 6 rally before the Capitol Riot, the younger Trump all but declared that the old Republican Party didn't exist anymore."

Trump told McDaniel he didn't care whether he destroyed the Republican Party.

"I'm done," Trump told McDaniel. "I'm starting my own party."

"You cannot do that," McDaniel told Trump. "If you do, we will lose forever."

"Exactly. You lose forever without me," Trump responded. "I don't care."

Trump viewed the destruction of the GOP as payback to party leaders who betrayed him, a source told Karl, but top Republicans made clear they would stop paying his legal bills from post-election challenges and render his email list worthless.

"It's a list Trump had used to generate money by renting it to candidates at a steep cost," Karl writes. "The list generated so much money that party officials estimated that it was worth about $100 million."

Five days later, Trump backed down from his threat, and both he and McDaniel denied Karl's account of their conversation.

"ABC Non News and 3rd rate reporter Jonathan Karl have been writing fake news about me from the beginning of my political career," Trump said in a statement. "Just look at what has now been revealed about the Russia, Russia, Russia hoax. It was a made up and totally fabricated scam and the lamestream media knew it. It just never ends!"

Trump threatened to destroy GOP in temper tantrum over election loss -- and start his own