Presidential historian: Kavanaugh hearings may have been the last straw for Nikki Haley

Chris Whipple, author of The Gatekeepers: How the White House Chiefs of Staff Define Every Presidency, suggested that the reason for the abrupt resignation of U.N. ambassador Nikki Haley was that she may have been disgusted by the "merciless" behavior of her fellow Republicans toward Dr. Christine Ford during the Brett Kavanaugh confirmation hearings.

Whipple rejected host Kasie Hunt's supposition that Haley had simply "burned out".

"I don't disagree that the job is a churn, it's 24/7 to be sure," he said. "But U.N. ambassadors do not burn out as a general rule."

He offered a number of possible explanations including worries about how a "bloody" midterm could impact her political future.

"She may also realize that almost everyone in the orbit of the president eventually is tarnished or destroyed with very few exceptions," he added. "So I think the timing was odd. Why announce now when it's not effective until end of the year? And the reason she gave is not credible to me."

Asked what he thought would be a believable explanation for her departure, Whipple did not hold back.

"It is even conceivable that she felt the spectacle of the Kavanaugh confirmation with that merciless attack on Dr. Ford was a bridge too far," he said. "That's sheer speculation on my part, but given her outspokenness in the past, who knows?"

Haley's resignation letter is dated October 3, 2018, just days before the Republicans advanced Kavanaugh's nomination to a full vote.

Watch the video below.