President Bush's new strategy of transferring power quickly to Iraqis, and his critics' alternatives, share a fundamental flaw: all commit the United States to a unified Iraq, artificially and fatefully made whole from three distinct ethnic and sectarian communities. That has been possible in the past only by the application of overwhelming and brutal force. President Bush wants to hold Iraq together by conducting democratic elections countrywide. But by his daily reassurances to the contrary, he only fans devastating rumors of an American pullout. Meanwhile, influential senators have called for more and better American troops to defeat the insurgency. Yet...