There may be no more vital aspect of a president’s character than the willingness to abandon deeply held beliefs when the facts demand it. For Johnson, whose primal fear of humiliation is rivaled only by that of Donald Trump’s, it meant giving up on the job he’d hungered for for decades.

For Richard Nixon, it meant heeding the advice of Republican leaders when the Watergate scandal overwhelmed him, rather than risking a constitutional crisis by rejecting a Supreme Court order to turn over the tapes that doomed him.

For Ronald Reagan, it meant acknowledging that in fact his administration had traded arms for hostages held by Iran. As he put it, in one of the more candid admissions of any president, “A few months ago I told the American people I did not trade arms for hostages. My heart and my best intentions still tell me that’s true, but the facts and the evidence tell me it is not.”

For George W. Bush, who’d launched the invasion of Iraq in 2003 on the premise that it would trigger a birth of freedom throughout the Middle East, it meant a radical change of policy—and a new defense secretary—three years later when that premise lay in ruins.