“[Donald] Trump’s second-place finish to Sen. Ted Cruz (Tex.) in Tuesday’s Wisconsin Republican primary may represent no ordinary setback,” write the Washington Post’s Karen Tumulty, Jose A. DelReal and Robert Costa. “It appears to be a pivot point—although it has yet to be seen whether the trajectory from here points downward or upward.”

That is an absolutely rock-solid analysis. The likelihood that it will be proved mistaken is zero, maybe less. As the Weekly Standard’s Mark Hemingway observes, it illustrates “why national...