Those campaign promises, as everyone is well aware, were generally more populist than the official G.O.P. agenda: Trump promised middle-class tax cuts and a generous Obamacare alternative, he stiff-armed the entitlement reformers and talked up infrastructure spending, and he railed against free trade deals with every other breath. And that populist branding was crucial to the electoral trade he made, which ceded a share of business-friendly suburbanites to the Democrats but reaped a crucial group of erstwhile Obama voters, mostly white and working class and concentrated in the Rust Belt and upper Midwest states, who ultimately handed Trump the presidency.

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. And their potential cost, for now, can be swallowed up by general economic growth or dealt with via cynical payoffs; if the general economic growth itself goes away, well, then Trump isn’t getting re-elected anyway.

If you expect this to lead to good policymaking, you haven’t been paying attention to how this White House operates. But the fact that Trump has this particular incentive to focus on free trade’s Midwestern losers is not itself a bad thing. One of the strongest arguments for the countermajoritarian element in the Electoral College is that it provides a point of leverage for regional populations that have suffered particularly at the hands of an overreaching bipartisan consensus. And the bipartisan consensus on trade with China really is ripe for an updating, since the domestic costs have been higher and geopolitical benefits more meager than the expert class predicted 20 years ago.