John Bolton told GOP donors that Trump is 'mentally unstable': report
Donald Trump (AFP Photo/Timothy A. Clary)

A new report from Vanity Fair's Gabriel Sherman sheds some more light on former national security adviser John Bolton's decision to blow up President Donald Trump's top defense against impeachment.

According to Sherman's sources, Bolton has told Republican donors that he believes Trump is "mentally unstable" and worries that the president could pull the United States completely out of NATO if he wins a second term.

Sherman reports that Trump allies are preparing to launch a furious counterattack against Bolton and his tell-all book that is scheduled for release on March 17th.

"He’s a bitter ex-employee," one former White House tells Sherman.

A source close to Secretary of State Mike Pompeo says that America's top diplomat may even get into the action as a character witness against Bolton.

"Pompeo and Bolton were at war with each other during the administration," the source explained. "Pompeo thought that Bolton was constantly trying to undercut him and the president."

Nonetheless, Bolton's revelation has made it all but certain that the Senate will call him to testify at the president's impeachment trial.

"[Senate Majority Leader Mitch McConnell is] resigned to the fact there will be witnesses," one Republican tells Sherman.