Donald Trump says he wants to unite the Republican Party, but he keeps acting as if he’s mounting a hostile takeover. He’s now threatening to blow up the party’s July convention because he and his campaign were too lazy or inept to understand the 50 state nomination rules.

That’s the story behind Mr. Trump’s complaints that the party’s nominating rules are “rigged” against him. “It’s a crooked system. It’s 100% corrupt,” the front-runner howled on Sunday following a Friday op-ed on these pages making the same claims. He...