The Aug. 6 debate marked the beginning of a new and more volatile phase of the contest: a wave of boomlets. The candidates who can surge — and stay at the top — could define the race. It represents a big test for the candidates who led the polls for much of the first half of the year, Jeb Bush and Scott Walker. Already, it’s one Mr. Walker is struggling to pass.

Carly Fiorina has made the largest leap in national polls, and Marco Rubio, Ben Carson and Ted Cruz appear to have made gains as well. But where the story really matters is in Iowa and New Hampshire, and in the so-called invisible primary for elite support. These three contests nearly amount to separate campaigns, with Iowa and New Hampshire something like two brackets in a tournament, and with the invisible primary bestowing the resources and credibility that help candidates reach the finals.

Mr. Bush and Mr. Walker appear to have lost ground in all of them.