Elections supposedly prevent convulsions, serving as safety valves that vent social pressures and enable course corrections. November’s election will either be a prelude to a convulsion or the beginning of a turn away from one.

America’s public-policy dysfunction exists not because democracy isn’t working but because it is. Both parties are sensitive market mechanisms, measuring more than shaping voters’ preferences. The electoral system is a seismograph recording every tremor of public appetite. Today, the differences that divide the public are exceeded by the contradictions within the public’s mind.