We could see a great party split in two. That, I think, is what I’m seeing among the Republicans, a slow-motion break. The question is whether it will play out over the next few cycles or turn abrupt and fiery in this one. Some in Washington speak giddily of the prospect, wondering aloud if the new party’s logo should be a lion or a gazelle. But America’s two-party system has reigned almost since its beginning, and it has kept us from much woe. It has provided stability, reliability and, yes, progress. The breaking or splintering of one of those parties would be an epochal event. Ross Perot in the 1990s was a one-off; the party soon enough healed back into one. Mr. Trump may be a one-off, but the divisions he’s revealed—on how on-the-ground and unprotected people feel about illegal immigration, on the deeper and more dangerous implications of political correctness, on a host of economic and cultural issues—will not, I suspect, be resolved so easily.

If the GOP breaks it will be bitter. The establishment thinks they are saving the party from the vandals—from Trumpian know-nothingism. But Republicans on the ground think those in the establishment were the vandals, with their open borders, donor-class interests and social liberalism.

The distance between the top of the party and the bottom has been growing for years, at least since 2008. The bonds between the two have stretched and stretched, and this year they began to snap. That’s the story of the year, that the snapping became obvious. Mr. Trump and the Trumps of the future are the result, not the cause. The establishment does not see this. They think it’s about him. It’s about them.