Regardless of the outcome of the midterm election, this much already has become clear: The battle for the soul of the Republican party is over, and President Trump has won.

Mr. Trump was long resisted by his party’s establishment, and rejected by a large swath of the GOP’s core ideological conservatives, many of whom formed a kind of never-Trump resistance.

Now, as the second anniversary of his election approaches, both of those opposition fronts have crumbled. For Republicans, for better or for worse, it’s Mr. Trump’s more-populist party now.

At the grass roots, Republicans have united behind Mr. Trump with surprising solidarity. In this campaign season, establishment GOP candidates have accepted his help and endorsement and, in many cases, mimicked his style and themes.

The furious Democratic opposition to Supreme Court nominee Brett Kavanaugh has galvanized even many Republicans dubious about Mr. Trump. They see him as a flawed but preferable alternative to a Democratic Party they dislike and fear, and appear to regard him as a useful shield against it.