“Bushes were to win, but not brag; succeed, but not preen,” Jon Meacham writes in his recent biography of the 41st president. Trump brags and preens through successes and failures alike. Bush had a capacity to laugh at himself. Trump does not. Bush had some money, and a lot of class. Trump has lots of money and no class.

Bush is profoundly decent. Trump is profoundly not.

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These contrasts don’t mean that Bush was without blemish: As Meacham notes, there were political misjudgments and calculated concessions to ambition on the long path to power. Nor does it mean that Trump doesn’t have his own kind of strengths, not the least of which is his loudly declared indifference to elite opinion.

Yet the fact that personal virtue does not always guarantee political success — or that private vice may often facilitate public achievement — does not mean countries can afford to remain indifferent to questions of virtue and vice. That’s what some of Bill Clinton’s liberal defenders argued during the impeachment debates in the 1990s, and what Trump’s defenders believe today.

They’re wrong. In an age of radical transparency, who the president is inevitably spills over into how he’s seen. Jack Kennedy might have been all class in public and a complete cad in private, but he lived in an era when he could get away with it.

Not anymore. Today’s presidents will be judged on their behavior, which is why the Trump brand is proving so damaging to the G.O.P.’s midterm prospects, despite the strength of the economy. Today’s presidents also model behavior, and tell every presidential aspirant what will or won’t work for them politically.