Will Virginia teach Trump fans a lesson?

Tuesday night’s losses could have a helpful effect on Trump enthusiasts. They imagine the number and strength of his supporters as bigger than it is. They imagine his opponents as unappreciative sellouts: Trump has won and will continue to win, you just don’t get it. After Virginia, they must surely see trouble. Donald Trump has not built support in the middle, he’s alienated it. The press’s antipathy to Mr. Trump is real and unchangeable, but you cannot blame all his problems on it. Pros get around the press, use it as a foil and straight man, and speak every day to independents, centrists and the softly aligned.

Mr. Trump has not been able to do this. It is the big story of the year since his election—that he has not a growing base but a smaller, so-far indissoluble core.

The parties are each in an existential crisis. The Democrats, split between the Sanders/Warren progressive vision and the old Clinton vision, will fight more passionately among themselves as 2020 approaches. The Republicans are left knowing that day by day, Mr. Trump is crashing. The wiser of them suspect that when he’s gone, what replaces him is nothing. Because the Republican Party is riven and no one knows what it stands for anymore.