Can the descent of American political culture into ugly tribalism be halted? Alabama voters will give their answer when they decide whether to send Roy Moore to the U.S. Senate. Moore, 70, has built a long, disgraceful career out of smarmy religiosity spiked with tribal grievance. Having posed for years as the most pious of Christians, he now stands accused by nine women of un-Christian behavior: They claim convincingly that Moore, when he was in his 30s, aggressively pursued romantic or sexual relationships, including with teens barely half his age. Successful demagogues can use tribal enmities to blind their followers...