Donald Trump — meet Kyrsten Sinema. Sen. Sinema (I-Ariz.) recently departed the Democratic Party to become an independent. If Trump follows her lead and runs for president as an independent he instantly launches the most consequential third-party candidacy in American history. Think about it. Polls now show GOP voters increasingly rejecting the disgraced ex-president as the party’s 2024 nominee. If Republicans turn on him, is there any doubt the notoriously thin-skinned Trump will soon start threatening a run as an independent to spite his former party? A third-party platform allows him to stay in the media spotlight and continue to...