Donald Trump’s damage to the Republican Party, although already extensive, has barely begun. Republican quislings will multiply, slinking into support of the most anti-conservative presidential aspirant in their party’s history. These collaborationists will render themselves ineligible to participate in the party’s reconstruction. Ted Cruz’s announcement of his preferred running mate has enhanced the nomination process by giving voters pertinent information. They already know the only important thing about Trump’s choice: His running mate will be unqualified for high office because he or she will think Trump is qualified. Hillary Clinton’s optimal running mate might be Sen. Sherrod Brown of Ohio,...