For several years now, the most powerful and mysterious force in American politics has been a free-floating populist rage. It's been directed at Washington and politicians this time, instead of at populism's traditional targets of Wall Street and businessmen. Stoked by radio-talk-show hosts, worshipped by fearful pols, the new populism created the movements for term limits and the balanced-budget amendment; turned Ross Perot's presidential bid from an eccentric billionaire's ego trip into a historic event; and ultimately led to last November's upheaval, in which Republicans won control of Congress for the first time in 40 years.
Predicting political trends is like...