Long before Donald Trump, the Republican Party had an obvious problem. Its core economic agenda — tax cuts, free trade, deregulation and a promise to shrink the federal leviathan — was seen by many Americans, including many of the party’s own voters, as distant from their concerns and too skewed toward the rich.

The last attempt to do something about this problem, George W. Bush’s compassionate conservatism, foundered with his presidency, and in 2008 and 2012 the party swung back to a more generic Reagan-era message, without particularly impressive results.

But going into the 2016 campaign there was a sense that the party might be ready to experiment anew. Two overlapping groups within the conservative intelligentsia — “reform conservatives” and “libertarian populists” — threw out a range of ideas for how a free-market party might shed some of its “party of the rich” baggage and deal more directly with middle-class anxieties. Various presidential candidates, from Marco Rubio to Rand Paul, Rick Perry and Jeb Bush, picked up on some of these proposals, in the clear hope of leaving the days of “you built that!” and “the 47 percent” behind.

Instead we got a different response to the G.O.P.’s economic policy problem: Trumpian populism, which won the votes of working-class Republicans and carried all (or at least a plurality) before it. And after Monday’s speech in Detroit, in which Trump — notionally — committed himself to a tax agenda, we can say definitively what Trumponomics represents.