That was the story of 2016; the story since, though, is one of reversion to the older political order. Because Trump has mostly governed as a conventional Republican, a certain kind of conventional Republican has come home to him, keeping his support stable in the states that the Romney-Ryan ticket won easily in 2012. But for the same reason — because the infrastructure plan never materialized and the tax cut was a great whopping favor to corporate interests and the health care repeal-and-replace effort was a misbegotten flop — the swing voters he needs to hold the Midwest are now drifting away.

And because Trump naturally alienates women and can’t make a gesture of outreach to blacks or Hispanics without stepping on it with bigotry the next day, he doesn’t really have another path back to the White House if those Obama-Trump voters in Michigan and Pennsylvania and Ohio go Democratic or stay home. Certainly the Republicans criticizing him on trade aren’t offering him such a path: Their overall vision is the same tired G.O.P. orthodoxy that went down to defeat in 2008 and 2012, and that Trump himself crushed in the last primary campaign.

So the fact that Trump’s tariffs are generally unpopular, even in Midwestern states, doesn’t matter politically nearly as much as their potential appeal to the narrow slice of blue-collar swing voters that he needs if he’s going to be re-elected.