Last summer, during the height of the presidential campaign—not the Biden v. Trump one, the Harris v. Trump one—I heard a rumor while in the MSNBC green room. Mark Cuban, the former owner of the Dallas Mavericks, Shark Tank stalwart, and indefatigable Democratic surrogate, had been asked to submit VP vetting papers by the Harris campaign. I never was able to nail down the rumor—until now. In an interview Thursday, Cuban confirmed that he was, indeed, asked. He also said that he declined the offer because his vetting book would be too long and it wasn’t worth the trouble for...