"United We Fall" argues that today's harmful levels of polarization in American politics can be ratcheted down only by giving up the twin notions that the center is the sweet spot for political efficiency and that all differences deserve equal weight in the democratic balance. The American people need instead to embrace a political credo of civic engagement, confrontation with open ears, and spirited debate. The commonplace United We Stand must be supplanted by the insight that democracy is strongest where it acknowledges and formalizes real division. But surely bipartisan rancor in...