'The floodgates are open': Bolton bombshells may force GOP senators to approve impeachment witnesses
John Bolton appears on Fox News (screen grab)

The leak of John Bolton's new book may force Senate Republicans to agree to additional testimony in the impeachment trial.

The former national security adviser revealed that President Donald Trump explicitly tied Ukraine aid to an investigation of Joe Biden, and GOP sources told Axios that new evidence would be enough to convince Republicans to approve witness testimony.

Bolton's book, "The Room Where It Happened," due out March 17, claims Trump told him "he wanted to continue freezing $391 million in security assistance to Ukraine until officials there helped with investigations into Democrats including the Bidens," according to the New York Times.

Trump denied those claims after midnight, and hours later falsely claimed that House Democrats did not call Bolton to testify, but GOP sources say the White House and party leaders fear what's coming next.

"There is a sense in the Senate that if one witness is allowed, the floodgates are open," one top aide told Axios. "If [Bolton] says stuff that implicates, say Mick [Mulvaney] or [Mike] Pompeo, then calls for them will intensify."