Enemies are useful: We all know the sweet, full-bodied relief of having someone else to blame for our problems. Why did the crops fail? It could be that you are an inept farmer. It could be that everything is up to chance. Or it could be that your neighbor, who has always been jealous of you, is doing something sinister to your crops.

Everyone does this, but Donald Trump does it with a special wronged fury. As a candidate, he obsessed over spectral forces that might deny him victory: phony polls, a calcified Republican establishment, vast voter-fraud conspiracies. He has brought the same instincts to his presidency, with increasingly self-defeating results. Last month, Trump embarked on his first big international trip as president. The itinerary included a major address to the Muslim world in Saudi Arabia and a much-anticipated NATO meeting — occasions that presented, for Trump, welcome opportunities to divert attention from the allegations of coordination between his campaign and Russia that heightened after he fired James Comey, director of the F.B.I. Instead, on the morning of May 18, one day after the Justice Department announced it was appointing a special counsel to investigate the matter, Trump fumed on Twitter: “This is the single greatest witch hunt of a politician in American history!”

“Witch hunt” seemed like a particularly Trumpish complaint — an unshakable belief in his own persecution leading him to compare his own experiences to vastly worse ones — and indeed, it was the fifth time since January that he had denounced one “witch hunt” or another on Twitter. But an obsession with the witch hunt long precedes him in American politics: In the last century, a parade of disgraced presidents and other public figures (almost all of them men) have also chosen to don this particular black mantle of victimhood. “Witch hunt” once meant persecution of the marginalized by the powerful. So how did it come to suggest something so nearly the opposite?