Establishment Republicans should keep the champagne on ice until after the midterm elections. Too many are already popping corks, pronouncing their strategy of “crushing” the Tea Party during the primaries as a crucial step in their successful takeover of the U.S. Senate. There are increasing signs, however, that the GOP might not take control of the Senate and may only make modest gains in the House of Representatives. In states like North Carolina, for example, the GOP candidate hasn’t shown the ability to wage a major-league campaign. In other key battleground states, the establishment GOP is supporting problematic candidates, like...