It was probably inevitable that Donald Trump and his media munchkins would alight on the stab-in-the-back theory to explain his probable defeat in November. The surprise is that they are doing so with the election still three months out.

“If in 96 days Trump loses this election, I am pointing the finger directly at people like Paul Ryan and Mitch McConnell and Lindsey Graham and John McCain and John Kasich and Ted Cruz,” Fox News host Sean Hannitytold his radio audience last week. “I have watched these Republicans be more...