According to people who know him well, Trump’s definition of loyalty is blunt. “Support Donald Trump in anything he says and does,” Roger Stone, the president’s longest-running political adviser, told me. “No matter what,” former Trump Organization executive Barbara Res said. “Or else,” added Louise Sunshine, a friend of Trump for nearly 50 years. “I think he defines it as allegiance,” biographer Tim O’Brien told me. “And it’s not allegiance to the flag or allegiance to the country—it’s allegiance to Trump.”

Congenitally untrusting, reared in the ruthless arena of pay-to-play, back-scratching (and back-stabbing) New York City politics of the 1960s, ’70s and ’80s, Trump was schooled and shaped by some of the most committed, effective and objectionable practitioners of quid pro quo. The self-interested sense of loyalty he developed then is transactional to the point of ephemeral, an almost always one-way street that can double as a revolving door—a kind of pliability that makes him seem at times something close to forgiving.

Taken as a whole, this mixture of traits makes Trump’s unprecedented presidency unprecedented in this respect as well, presidential historians told me. Presidents all require loyalty—up to a point. And they have to show loyalty—except when they shouldn’t. Too much loyalty can be just as detrimental to a president and his administration as too little.