The change in results on the generic ballot question for the 2016 race reveals an interesting pattern. Data from YouGov, an online polling organization, show that once Mr. Trump began to dominate the Republican primaries in March and a concerted effort by the other candidates began — and then failed — there was a significant shift in the generic ballot results.

From autumn 2015 to spring 2016, the Republican was beating the Democrat in the generic ballot question. In January 2016, for example, the spread was seven points — 39 percent for the Democrat and 46 percent for the Republican. As it became clear that Mr. Trump would be the nominee, the pattern changed and the Democratic candidate went ahead. By the end of July, the Democrat had 44 percent and the Republican 36 percent — a complete reversal.

One way to view this switch is as the price for nominating Mr. Trump.