The emergence of the modern presidency in the first half of the twentieth century transformed the American government. But surprisingly, presidents were not the primary driving force of this change—it was Congress. Through a series of statutes, lawmakers endorsed presidential leadership in the legislative process and augmented the chief executive’s organizational capacities.   But why did Congress grant presidents this power? In Power Shifts, John A. Dearborn shows that legislators acted on the idea of presidential representation. Congress subordinated its own claims to stand as the nation’s primary representative institution and designed reforms that assumed the president, selected by the country rather than states or districts, was the superior steward of national interest. In the process, Congress recast the nation’s chief executive as its chief representative.   As Dearborn demonstrates, the full extent to which Congress’s reforms rested on the idea of presidential representation was revealed when that notion’s validity was thrown into doubt. In the 1970s, Congress sought to restore its place in a rebalanced system, but legislators also found that their earlier success at institutional reinvention constrained their efforts to reclaim authority. Chronicling the evolving relationship between the presidency and Congress across a range of policy areas, Power Shifts exposes a fundamental dilemma in an otherwise proud tradition of constitutional adaptation.