As the members of North Atlantic Treaty prepare to mark next week the alliance’s 75th birthday, it’s hard to know whom the allies see as a bigger threat — President Putin or President Trump. What else to make of the recent obsession with “Trump-proofing”? Such proofing is needed, a former American envoy says, because the alliance “is bound to be disrupted” by a re-elected Trump, “who is not interested” in “being managed himself or managing an alliance.”