What if Donald Trump has to fight a grudge match against Liz Cheney and Chris Christie on his way to a second term? This scenario is probably more likely than you might think—one with significant consequences. Both Cheney and Christie are tough pugilists, and both are in the news flirting with a presidential run. In a sense, they are already running against him. This past week, Cheney traveled to Manchester, New Hampshire, and delivered a “standing ovation” speech that was interpreted by CNN as “testing the waters” for a presidential bid. During the speech, she staked out conservative ground criticizing...