Trump aide told lobbyist he feared people underestimated what the president was capable of: new book

One of the many former chiefs of staff to Donald Trump was secretly warning D.C. Republicans that the president could become volatile if he loses the 2020 election.

The new book "This Will Not Pass" by Alexander Burns and Jonathan Martin details the final months before the election, with Mulvaney being relegated to "a largely ornamental position as special envoy for Northern Ireland."

The book cited "former colleagues" who believed Mulvaney to be "a brittle know-it-all." But when he spoke with "the head of an influential Washington business lobby," he revealed his real concerns about what might happen if Trump lost.

"Speaking with Josh Bolten, the former White House chief of staff to George W. Bush and now chief of the Business Roundtable, Mulvaney said he was worried that people were underestimating what the man he served was capable of," said the book, which became publicly available on Tuesday.

RELATED: Donald Trump derided Melania’s looks during meeting with GOP strategists

“If Trump loses,” Mulvaney said, “I’m not sure he’ll leave office willingly.” The book described Mulvaney as one of the "people close to Trump" who kept their "fears private until it was far too late."

CBS News was recently denounced by media watchdog group Media Matters as "an embarrassment" for hiring Mulvaney.

"Mulvaney as OMB director carried out Trump’s order to withhold nearly $400 million in military aid to Ukraine around the same time the president was pressuring the country’s president, Volodymyr Zelenskyy, to investigate his then-presidential opponent, Joe Biden, and his son, Hunter Biden," Vanity Fair recalled in March.

In a recording obtained by Washington Post's Jeremy Barr, it was revealed the only reason CBS hired Mulvaney was so when Republicans took over the House and Senate they would have inroads.

“If you look at some of the people that we’ve been hiring on a contributor basis, being able to make sure that we are getting access to both sides of the aisle is a priority, because we know the Republicans are going to take over, most likely, in the midterms,” said Neeraj Khemlani, the news division’s co-president, in the recording. “A lot of the people that we’re bringing in are helping us in terms of access to that side of the equation.”

NOW WATCH: Republican grills legal expert over Supreme Court’s integrity -- and she throws GOP’s antics back in his face

Republican grills legal expert over SCOTUS integrity, and she throws GOP’s antics back at himwww.youtube.com