Donald Trump established a template for stealing a presidential election that Republicans will have four years to enact ahead of the next contest, according to the author of a new book on his final days as president.

Robert Costa, co-author of the new book, "Peril," with his Washington Post colleague Bob Woodward, told NPR that Trump stunned then-vice president Mike Pence by issuing a statement Jan. 5 declaring that he would carry out the unconstitutional plot to overturn the election.

"This is where you start to see the crack in the American democratic system — when the vice president and president are not in sync, and the president starts to speak for other constitutional officers," Costa said. "This is where Pence and his team really go into a bunker mode and they don't even share the letter Pence ultimately releases on Jan. 6, explaining his decision to not try to do anything crazy on Jan. 6. They don't even share it with the White House counsel or with Trump. That was the level of tension between the president and the vice president."

Conservative legal scholar John Eastman had written a legal memo arguing that Pence had the authority as vice president to reject slates of electors for Joe Biden, throwing the election to the House of Representatives, but Costa said the vice president declined to go along because there were no alternate slates of electors.

"They were trying to get [vice president] Pence and others to move the election to the House of Representatives to block Biden from taking office," Costa said. "Imagine if in January 2025 Republicans are much more organized and they have alternate slates of electors ready in many states. What happens then?"

Author reveals what drove Pence into 'bunker mode' before Jan. 6