The pattern of multilateral engagement and unilateral retrenchment in American foreign policy from the Cold War through the Clinton, Bush, and Obama years presents a puzzle. What accounts for the unilateralist turn? Is it a passing aberration attributable to the neoconservative ideology of the Bush administration? What then of the disengagement evident earlier during Clinton's presidency, or its continuation under Obama? Was the U.S. investment in multilateral institutions following World War II an anomaly? Or is the more recent retreat from international institutions the irregularity?