Former Defense Secretary Mark Esper says the biggest threat facing America isn’t Russian aggression, the global pandemic or an increasingly menacing China. It’s “extreme political partisanship” in Washington.

Esper, a lifelong Republican, argues lawmakers need to take less extreme positions on either side of the political aisle, which he says is the only way to break the “resulting dysfunction” in Washington and advance the nation’s interests. He decries intraparty feuding while calling out his former boss, Donald Trump, for divisiveness and a lack of “core principles and integrity.”

“We need to pay less attention to the wings on these parties and more focus on the folks in the middle, whether it’s Democrat or Republican,” Esper said.

In response to comments Esper made on “60 Minutes,” the former president called Esper a “lightweight” and “RINO,” that is, a “Republican in name only.”

“I’m far more Republican than Donald Trump is,” Esper shot back in an interview with CBS News chief Washington correspondent Major Garrett on Monday.

Esper’s new memoir “A Sacred Oath,” published by a division of Paramount Global, chronicles his time as Army secretary and defense secretary from 2017 to 2020. He says he resisted the former president when Trump asked if the military could fire missiles at a Mexican drug lab or if it were possible to shoot protesters in D.C.

But Esper has been accused of waiting until the publication of his book to disclose such explosive allegations about Trump – some two years after the events transpired.

“If I spoke up at the time, I would be fired. And my concern was if I was fired, there would be somebody else put in my place who would most likely or more likely be willing to do some of these things,” Esper said, arguing he was positioned to play defense against “dumb ideas.”

In December of 2020, about a month after leaving office, Esper said he started writing the book which he finished by spring. It then got held up in the Pentagon pre-publication review process, and he later sued the Pentagon over redactions to certain passages.

Esper said he never defied a presidential order because Trump so rarely gave them. Instead the former president would “rant…he would suggest and he would press,” but those diatribes almost never resulted in tangible directives.

Esper was among the Trump officials who posed for a photo at a church near the White House after law enforcement cleared racial justice protesters from Lafayette Park in June of 2020. He now admits that was a mistake.

Faced with criticism that he aided and abetted Trump’s worst tendencies, Esper argues he was a bulwark against them and that the book is a roadmap for future secretaries of defense if they face the same pressures he did.

“If good people don’t serve or if you want the good people to leave the cabinet, then who are you left with,” he said. “I mean, by definition, you’re only left with the bad people, and that’s not good for our country.”