For decades, Donald Trump has depended on loyalists to take care of especially sensitive and difficult tasks. These guardians of his image—including the Red-baiter Roy Cohn, the tabloid publisher David Pecker and the lawyer Michael Cohen—learned a hard lesson from their service. They pledged fealty to Mr. Trump and dedicated themselves to shielding him. For a while, they became wealthier and more powerful through their association with him. But Mr. Trump ultimately offered little back in protection or respect.

Mr. Trump’s...