The Constitution's framers gave the Senate a share of the treaty-making power in order to give the president the benefit of the Senate's advice and counsel, to check presidential power, and to safeguard the sovereignty of the states by giving each state an equal vote in the treaty-making process. The constitutional requirement that the Senate approve a treaty by a vote of two-thirds of senators present means that treaties must overcome political and partisan divisions to gain approval.
During the summer of 1787, delegates to the Constitutional Convention debated whether the power of treaty making should reside within the legislative or executive branch. Under the Articles of Confederation, a treaty could be entered into with the consent of nine of the thirteen states, or two-thirds of the total number of states. Some delegates, such as South Carolina's Charles Pinckney, urged that the Senate, in which each state had equal representation, should have the sole power to make treaties. Alexander Hamilton argued that the executive branch should exercise powers related to foreign relations and should therefore have the power to make treaties "with the advice and approbation of the Senate." In the end, Hamilton's argument proved to be the most persuasive.
When the Senate first convened on March 4, 1789, it was unclear what the exercise of the Senate's advice and consent power would look like in practice. The Senate and President George Washington initially resolved to confer in person prior to negotiating new treaties. On August 22, 1789, Washington and Secretary of War Henry Knox arrived at the Senate Chamber seeking the Senate's advice on negotiating a treaty with Native American tribes. They submitted a series of questions for the Senate's consideration. The Senate voted to refer the questions to a committee rather than debate the issue in the presence of the president. Irritated, Washington decided that in the future, he would send communications regarding treaties in writing, setting the precedent that all of his successors have followed.
The Senate approved for ratification one of the most contentious treaties in U.S. history during the Washington administration. At the urging of Federalist Party senators, in 1794 the president sent Chief Justice John Jay to London to settle open disputes with Great Britain. The Senate agreed to the appointment of Jay as envoy, but Washington did not consult the full Senate on instructions for negotiating the treaty. When the Jay Treaty was submitted to the Senate for approval in 1795, the treaty's opponents, mostly Jeffersonian Republicans, demanded that the terms of the agreement be re-negotiated, but Federalist senators defeated that plan and secured its approval on June 24, 1795.
In later years, some presidents sought to prime the Senate for approval of a treaty by appointing senators to negotiating delegations. During the War of 1812, for example, Delaware senator James Bayard was a member of the delegation that negotiated the Treaty of Ghent. It was approved by the Senate unanimously. A century later, senators criticized President Woodrow Wilson for not including members in the delegation that negotiated the Treaty of Versailles, which ended World War I and established the League of Nations. The Senate ultimately rejected the treaty in November 1919 after months of heated debate.
With the Treaty of Versailles in mind, Wilson's successor, Warren G. Harding, appointed Senator Henry Cabot Lodge and Democratic Leader Oscar Underwood as delegates to the Washington Naval Conference in 1921, thereby improving the likelihood of Senate approval. Indeed, all three of the treaties negotiated during that conference were approved for ratification. For much the same reason, Presidents Franklin Roosevelt and Harry Truman involved the Senate Foreign Relations Committee chairman, Tom Connally, and the ranking Republican, Arthur Vandenberg, in the creation of the United Nations. This action helped to spare the UN the fate of the League of Nations; there were only two Senate votes against its charter.
Until 1929 the Senate deliberated on treaties in closed-door executive sessions. Despite the secrecy of these sessions, newspapers frequently published leaked accounts of the debates, occasionally printing the text of a treaty before senators received their official copies. The Senate investigated, fretted, and protested, but proved powerless to stop the leaks, which likely came from the senators themselves. Finally, in 1929, the Senate opened executive sessions to the press and the public. Today, the Senate holds closed sessions only under the rarest of circumstances, usually to deal with classified information.
Since the end of World War II, the United States has increasingly entered into international agreements known as "executive agreements." Although they are not submitted to the Senate for advice and consent, they are binding under international law. While presidents have utilized these executive agreements since the 1790s, they became more common in the 20th century due, in part, to the sheer volume of business conducted by the Senate and the difficulty of getting expedient action on formal treaties. In many cases, Congress has passed legislation authorizing executive agreements in areas like foreign aid and trade. Since 1990, only about 6 percent of international agreements have been made through formal treaties submitted to the Senate for advice and consent.