In 1955, William F. Buckley Jr. famously declared that the purpose of conservatism was "to stand athwart history, yelling 'Stop,' at a time when no one is inclined to do so, or to have much patience with those who so urge it." That astoundingly witty remark was a rueful acknowledgement of the uphill challenge facing the nascent American right, half a century ago — trying to halt the forward movement of a self-confident liberal left that was utterly certain it could make the world a better place through government action and forced social change. Who could have imagined, reading Buckley's...