A decade ago, I arrived in Antananarivo, the capital of Madagascar, for my first stint of field research into the island’s volatile politics. While unpacking in my hotel room, I heard sporadic celebrations erupting in the streets below. Confused, I asked a jubilant man what was going on. “The army captured the militia’s sorcerer,” he told me. “The president just announced that soldiers seized all of the sorcerer’s diabolical objects—and they’ll soon be destroyed.” Heavily armed criminal militias, known as the dahalo, had been terrorizing civilians in rural Madagascar. Now their sorcerer was in custody, and his talismans were broken and burned. The government and the public believed that the dahalo had suffered a severe blow, and that a more peaceful future was possible. The president, who had been in a precarious state politically, got a much-needed popularity boost. The lesson was obvious: Whether the sorcerer or the talismans really had powers didn’t matter. What mattered was what people believed. Beliefs, true or false, rational or irrational, shape politics. Elizabeth Bruenig: This Halloween, let’s really …