There is an old TV show called Unsolved Mysteries, which examined issues from UFOs to the disappearance of individuals. At the end of each segment, its host, actor Robert Stack, would implore, “If you have any information that can help us solve this mystery, please contact us.” One mystery that would have been perfectly suited for that show is why did Congress repeatedly, over nearly a half-century, delegate its own legislative authority to the presidency and the executive branch? Alas, this mystery has been solved by John Dearborn’s outstanding book Power Shifts.

As Dearborn notes, “No institution of American government has been more profoundly reshaped by ideas than the presidency” (p. 1). Many works focus on presidential power, with a primary examination of the expanded use of unilateral power. Such studies provide a wealth of information, but they do not address a key question: Why did Congress consistently delegate its own authority to the executive branch? According to the theory of checks and balances, each of the three branches is supposed to guard its own power. Rather than explaining this phenomenon, many scholars merely note its existence. Although there have been some excellent studies of this development, particularly James Sundquist’s work on the decline and resurgence of Congress, it has been a largely neglected area of study, until now.

One of the key ideas that Dearborn draws from the larger literature on the presidency is that presidents are “power maximizers” (p. 4). This is true of the presidency, but the same logic also should apply to Congress. After all, why should it delegate its authority, such as the ability to create a budget, to the president? The Constitution is clear in designating the power of the purse, one of the most important of all powers, to the legislative branch. Why then, provide presidents with a first-mover advantage in this area? And why should Congress give the president fast-track authority to negotiate tariffs? Because the power of the purse is one of Congress’s most important responsibilities, and if Congress is a power maximizer, this transfer of power makes no sense whatsoever.

Therefore, various explanations have been offered. Perhaps it was because Congress confronts a collective action problem. Or delegated power to the presidency only in times of unified government? Or perhaps only the president’s partisans supported such reforms, while the party out of power vehemently opposed them? Such explanations sound reasonable, yet Dearborn convincingly demonstrates that they are insufficient to explain Congress’s continuing pattern of delegating authority. First, although Congress does have a collective action problem, there were institutional alternatives other than delegating authority to the president. They could have set up committees to deal with this issue, as they eventually did in the 1970s. Another possible explanation is that Congress only delegated its authority during periods of unified government, with a president of its own party in the White House. As Dearborn shows, even though many reforms occurred during unified government, others occurred during divided government. Perhaps then it was a matter of how many seats the president’s party controlled. Yet, even though presidential partisans did indeed overwhelmingly support delegation, so too did members from the opposition party. Although each of these explanations is tantalizing, they simply do not hold up to empirical scrutiny.

So what is the answer? Maybe Congress did not realize what it was doing: it may have believed that it was not giving away its power. But again, the evidence suggests that many members identified the fact that these delegations of authority would indeed have the effect of increasing presidential power at the expense of Congress’s constitutional authority. By creating various institutions, such as the Bureau of the Budget, the National Security Council, and the Council of Economic Advisers in the executive branch, as well as providing presidents with broad reorganization authority, Congress established the basis for the modern presidency, an institution that would carry over from one president to another, thus establishing a permanent foundation for the expansion of presidential power. In so doing, Congress knew what it was doing, but once again we are left with the tantalizing question: Why did they do it?

Dearborn’s answer is ingenious, and his support for it from contemporary sources is convincing. He writes, “Central to legislators’ actions were their own understandings of the likelihood of presidents acting in the national interest” (p. 11). The Founders had no such idea of the presidency. Rather than the direct election of the presidency, they established an elaborate electoral college system to separate the public from election of the president. The idea that presidents are the tribunes or stewards of the American people can be found in the presidencies of Thomas Jefferson, Andrew Jackson, and Theodore Roosevelt, however. Jackson noted that only the president is elected by the entire nation, and therefore it is only the president who represents the nation as a whole. Alternatively, members of the House represent districts, and senators represent individual states. Hence, their interests are particularistic, whereas those of presidents are national. Such ideas have been ably expressed before by Douglas Kriner and Andrew Reeves in their work on particularistic presidents, as well as in William Howell, Saul Jackman, and Jon Rogowski’s work regarding nationalizing politics. Drawing on these works, Dearborn summons considerable historical evidence, mostly from the Congressional Record, to demonstrate that legislators of both political parties, in times of both unified and divided government, supported delegating authority because they believed that only the president represents the national interest. Furthermore, this pattern continued from at least 1910 through 1949 with the establishment of the Defense Department, the Central Intelligence Agency, and the National Security Council. These three institutions provided presidents with significant information advantages over Congress in foreign affairs. This was a major transfer of power to the presidency.

Dearborn then solves yet another mystery. Why did Congress change course beginning in the 1970s by passing a series of laws that challenged presidential authority, and why did it begin to develop its own institutional resources to offset the president’s information advantages? The answer is that Vietnam and Watergate undercut trust in the presidency. Analyses of presidential approval ratings show a consistent decline beginning in the 1960s, and work by Marc Hetherington demonstrates that trust in the federal government began to decline at the same time.

As a result, the idea that presidents represented the entire nation was challenged by more obstreperous members of Congress and by a new assumption, particularly from 1973 onward: Congress needed to hold presidents accountable. Again, using various sources, Dearborn demonstrates that the viewpoints of legislators of both political parties changed. The key explanation then for both the broad delegation of congressional authority to the president and the counterrevolution to limit such discretion was the existing perception of the president’s ability to represent the entire nation. And as we move toward a time when the presidents of both parties regularly see their approval ratings under water—that, is below 50% for much of their presidencies—the idea that the president represents the nation as a whole has become a subject of considerable debate and scholarly concern.

In his remarkable book, Dearborn provides copious primary source evidence to support his thesis, and each of the case studies presents new and important information for understanding one major facet of the expansion of presidential power. Needless to say, were Robert Stack still alive, he would deem this particular mystery as solved. It is a fascinating book that is appropriate for classes at the undergraduate and graduate level and is a terrific read for individuals interested in the subject of presidential power.