But he was an unpopular candidate in 2016, and still managed to win, however narrowly. His victory came even though large majorities of voters didn’t like him personally, didn’t believe he had the temperament to be president and didn’t think he was qualified for the job. Trump wouldn’t be president unless at least some people who held all of these negative views of him voted for him anyway.

To win reelection, he’ll probably need this to happen again. Which means he’ll need an opponent who, by Election Day, is as unpopular as Hillary Clinton was in November 2016, when 54 percent of voters said they had an unfavorable view of her.

It may be the single most important variable in determining Trump’s reelection fate. Is there a Democrat who can engage in months of direct combat with Trump and emerge with anything like the kind of popularity Barack Obama had in 2012 when a majority viewed him favorably? Or does the tribalized political and media culture of the Trump-era ensure that anyone who steps into the arena with him will end up in the same shape as Clinton?