Why this decrease? The rise of partisanship is one important reason. Although foreign policy has never been fully isolated from politics, political polarization began to rise in the 1970s, and it increased sharply in the 1990s. Today, members of Congress reflexively support their own party. In periods of unified government, this means extreme deference to the president. In periods of divided government, it means congressional gridlock. Neither scenario yields much in terms of congressional oversight.
Polarization also gives presidents reason to simply ignore Congress when making foreign policy. As the political scientist Kenneth Schultz has argued, with members less willing to cross the aisle, it is “more difficult to get bipartisan support for ambitious or risky undertakings, particularly the use of military force and the conclusion of treaties.” And so presidents opt for alternatives such as executive agreements over formal mechanisms such as ratified treaties. Consider the Iran nuclear deal. In 2015, President Barack Obama, concerned that he could not get a treaty with Iran past the Republican-controlled Congress, chose to make an executive agreement (which made it all too easy for Trump to tear up the deal later).
Another trend that has sapped Congress’ influence is the decline of congressional expertise on foreign policy and national security. Simply put, legislators used to know more about foreign policy than they do now. Greater expertise strengthened Congress’ formal and visible role, since committees could engage in greater oversight of the executive branch. Expertise also reinforced Congress’ invisible means of constraining presidential power. Presidents had to think about how a seasoned committee chair or member would assess a policy. During his initial escalation of the Vietnam War, for example, President Lyndon Johnson was careful to maintain the support of powerful committee chairs, such as Senator J. William Fulbright, who led the Senate Foreign Relations Committee from 1959 to 1974. Fulbright shepherded the Gulf of Tonkin Resolution through the Senate in 1964, but two years later, his probative hearings helped shift public opinion against the war.
Congressional expertise also led to serious, bipartisan policies that could force the president’s hand. A good example is the Cooperative Threat Reduction Program, an initiative for safely securing and dismantling weapons of mass destruction in the former Soviet Union. Senator Sam Nunn, a Democrat from Georgia, and Senator Richard Lugar, a Republican from Indiana—two defense stalwarts who had been deeply involved in arms control agreements during the Cold War—proposed it in 1991 as an amendment to the annual defense bill. The George H. W. Bush administration initially opposed the legislation because it diverted $500 million previously authorized for other purposes, but Nunn and Lugar prevailed, backed up by 86 votes in the Senate. They were able to pass their bill because the existing polarization was still manageable and because both senators were respected experts on defense and foreign policy.
The program was a high-water mark of expertise-informed legislation. In the years since, legislators have become less and less interested in the details of foreign policy. In 1994, a small group of newly elected congressional Republicans even proudly declared that they did not own passports.
Several factors explain the decline in expertise. Changes in the way senators now divide up committee roles, by increasing the number of committees they sit on, have led to greater breadth at the expense of depth. The media, facing fragmentation and declining budgets, have paid less attention to the crucial committees, especially the Senate Foreign Relations Committee and the House Foreign Affairs Committee, thus diminishing their value as reputation burnishers on Capitol Hill. Increased turnover has led to less seniority, particularly on the Senate Foreign Relations Committee, reducing the number of specialists to whom other senators can look for leadership on complex issues. Add in polarization and gridlock, which, by reducing overall congressional activity, also reduces the incentives to develop specialties, and the result is a Congress with decidedly less expertise.