Diplomacy in the American political system is frequently described as the exclusive province of presidents. Thomas Jefferson, America’s first secretary of state, wrote in 1790, “The transaction of business with foreign nations is executive altogether. . . . Exceptions are to be strictly construed.” A decade later, John Marshall, who would go on to become the most influential chief justice in U.S. history, declared on the floor of the House of Representatives, “The president is the sole organ of the nation in its external relations, and its sole representative with foreign nations.” Justice George Sutherland noted Marshall’s claim in United States v. Curtiss-Wright Export Corporation (1936), perhaps the most frequently cited case dealing with foreign affairs, concluding that the president “alone negotiates: Into the field of negotiation, the Senate cannot intrude; and Congress itself is powerless to invade it.”
The practice of American diplomacy, however, has always been far more complicated than the words of Jefferson, Marshall and Sutherland suggest. The ongoing negotiations over Iran’s nuclear program offer a textbook example. As U.S. negotiators meet with their Iranian counterparts in Geneva, administration officials back in Washington lobby Congress to set aside tough new sanctions legislation that would complicate, if not kill, the talks. Meanwhile, the White House knows it must craft its offer to Tehran with an eye toward what will be acceptable to a Congress that could be asked to repeal sanctions already on the books. And while administration officials play the inside game on Capitol Hill, they also play the outside game in the media against critics who have taken to the airwaves to argue that Iran can never be trusted.
The broader lesson here is that while Congress has no direct role in the conduct of diplomacy, it has ample indirect means to shape what presidents say to foreign governments or if they say anything at all. The Senate can refuse to consent to treaties. Congress can use its power of the purse and its power to legislate to constrain the president’s freedom of maneuver or even impose a new approach entirely. Lawmakers can influence public opinion and thereby dissuade presidents from pursuing their favored policies. And at times lawmakers may even invade the field of negotiations, Sutherland’s injunction notwithstanding. In short, while Congress takes a back seat to the president when it comes to diplomacy, it nonetheless can still have a say over the diplomatic road the United States travels.