We live in a time of tribes. Not of ideologies, parties, groups, or beliefs—these don’t convey the same impregnability of political fortifications, or the yawning chasms between them. American politics today requires a word as primal as “tribe” to get at the blind allegiances and huge passions of partisan affiliation. Tribes demand loyalty, and in return they confer the security of belonging. They’re badges of identity, not of thought. In a way, they make thinking unnecessary, because they do it for you, and may punish you if you try to do it for yourself. To get along without a tribe makes you a fool. To give an inch to the other tribe makes you a sucker.