Why has U.S. grand strategy persisted since the end of the Cold War? Despite shocks such as the 2008 global financial crisis and the costs of the war in Iraq—circumstances that ought to have stimulated at least a revision—the United States remains committed to a grand strategy of “primacy.” It strives for military preponderance, dominance in key regions, the containment and reassurance of allies, nuclear counterproliferation, and the economic “Open Door.” The habitual ideas of the U.S. foreign policy establishment, or the “Blob,” make U.S. grand strategy hard to change. The United States' military and economic capabilities enable the U.S. government to pursue primacy, but the embedded assumptions of the Blob make primacy the seemingly natural choice. Thanks to the Blob's constraining power, alternative grand strategies based on restraint and retrenchment are hardly entertained, and debate is narrowed mostly into questions of execution and implementation. Two cases—the presidency of Bill Clinton and the first year of the presidency of Donald Trump—demonstrate this argument. In each case, candidates promising change were elected in fluid conditions that we would expect to stimulate a reevaluation of the United States' commitments. In each case, the Blob asserted itself successfully, at least on the grand strategic fundamentals. Change in grand strategy is possible, but it would require shocks large enough to shake the assumptions of the status quo and a president willing to be an agent of change and prepared to absorb the political costs of overhauling Washington's traditional design.