On the opposite end of the Trump-impact spectrum is John Cox, a Republican businessman running for governor of California. With registered Republicans down to 25 percent of the Golden State electorate (putting them slightly behind independent voters), the party is as likely to capture the governorship this year as Jeff Sessions is to be the next head of the American Civil Liberties Union. Nonetheless, Republicans needed a candidate at the top of the ticket to increase turnout for all the down-ballot House seats they’re fighting over. With the state’s wacky primary system, in which the top two vote-getters advance to the general election regardless of party affiliation, that was hardly a given. (A longtime senator, Dianne Feinstein, will be facing a fellow Democrat.) But late in the race, Mr. Trump came out strongly for Mr. Cox, tweeting his praises, energizing the troops and propelling him to a solid second place behind Gavin Newsom, the Democratic lieutenant governor.

It is, of course, not unusual for presidents to have political coattails — and for the party wandering in the wilderness to show greater openness to new ideas and new kinds of candidates. The Democratic approach may be more a function of default (or desperation) than design, but Ms. Pelosi still deserves props for not seeking to kneecap candidates, like Conor Lamb in Pennsylvania and Mikie Sherrill in New Jersey, who have said they would not support her as speaker. With a bit of luck, genuine ferment and debate among Democratic candidates and officeholders over the right direction on issues like trade and immigration might result in at least one party oriented around a set of ideas.

Assuming that American democracy endures, a party organized around a single extreme personality seems like a brittle proposition. But Mr. Trump’s grip on the Republican psyche is unusually powerful by historical standards, because it is about so much more than electoral dynamics. Through his demagogic command of the party’s base, he has emerged as the shameless, trash-talking, lib-owning fulcrum around which the entire enterprise revolves.

Forget the longstanding Republican orthodoxy about the wonders of free trade. If Mr. Trump says tariffs are the way to go, his base is good with that. Even Republican lawmakers who fear a trade war seem disinclined to push very hard to prevent one. (Mitch McConnell, the Senate majority leader, has dismissed proposed legislation aimed at curbing the president’s tariff fever as an “exercise in futility.”)