Elbridge “Bridge” Colby is, as Donald Trump might say, straight out of central casting for a member of D.C.’s foreign policy elite. He has degrees from Harvard and Yale, a membership to Washington’s Metropolitan Club and the kind of coiffed hair and clipped accent that you’d expect from an American blue-blood. So pristine is his pedigree — his grandfather was head of the CIA — that a lightly fictionalized version of him appears in the New York Times columnist Ross Douthat’s memoir of his undergraduate years at Harvard, titled Privilege. But Colby, far from being a deep state darling, is...