When the Senate confirmed Brett Kavanaugh 50-48, it was a victory over American politics’ most vicious smear campaign in decades. Or was it? The left failed to keep Judge Kavanaugh off the Supreme Court, but it did irrevocable damage to his reputation and to America’s institutions—for which it has paid no price.

The left opposed Judge Kavanaugh from the start. Minutes after President Trump named him, leftist groups had dispatched protesters to the Supreme Court’s steps. Weeks later, activists flew into Washington, where they...