How Trump could fall short of his delegate target

But Mr. Trump’s lead could close if the votes from his opposition consolidate further. And there are signs of that.

Mr. Trump’s impressive showing in Illinois, Missouri and North Carolina last Tuesday led a lot of people to overlook just how strong Mr. Cruz really was. Mr. Cruz hit 40 percent of the vote in Missouri, something he had done only in Texas, in caucus states and in the Mormon areas of eastern Idaho. He hit 37 percent of the vote in North Carolina and swept the metropolitan parts of the state, usually an area of weakness for Mr. Cruz. He even won 30 percent of the vote in Illinois — again, something he hadn’t done in a blue-state primary (although he still showed considerable weakness in the core of the Chicago metropolitan area).

The easiest explanation is that Mr. Cruz was consolidating the conservative voters of a weakening Marco Rubio, who dropped out after Mr. Trump trounced him in the Florida primary. Mr. Cruz’s advance into the 30s puts him within striking distance of Mr. Trump in a lot of states where Mr. Trump might have been a big favorite earlier in the year. It would not take too many additional gains for Mr. Cruz to turn key states into tossups, or even to win them.

In this scenario, Mr. Trump barely wins states where Mr. Cruz is fairly strong, including winner-take-all contests in South Dakota, Montana and Arizona. If Mr. Trump lost those states, he would probably fall short of 1,237.