The Two-Thirds Supermajority
The core requirement lives in Article II, Section 2 of the Constitution. It states the President has the power to make treaties 'by and with the Advice and Consent of the Senate, provided two thirds of the Senators present concur'. This language is specific and demanding. 'Advice and Consent' means the Senate must formally approve a treaty for it to be ratified. It doesn't just rubber-stamp a presidential decision. In today's 100-member Senate, 'two-thirds of the Senators present' means that if all senators vote, a treaty needs 67 'yea' votes to pass. This supermajority is a far higher hurdle than the simple majority (51 votes) needed for most legislation. Technically, the Senate doesn't 'ratify' the treaty itself; it passes a 'resolution of ratification'.
If that resolution gets 67 votes, the treaty goes back to the President, who then finalizes the agreement with the other nation, officially making it law. Once ratified, a treaty carries the same weight as federal law under the Constitution's Supremacy Clause.
A Deliberate Check on Power
Why make it so difficult? The Framers of the Constitution were deeply suspicious of both unchecked executive power and entangling foreign alliances. They had just fought a war to escape a monarchy and were wary of giving any single person, including the president, the king-like power to commit the new nation to foreign obligations. At the time, specific regional interests, like fishing rights in the North Atlantic, also fueled the desire for a high bar to ensure no single region could sell out another's interests in a treaty. The two-thirds rule was a compromise. It gave the President the lead in negotiating with other countries but ensured that any major, long-term commitment would need broad, bipartisan buy-in from the Senate, where every state has an equal voice. It was designed to force deliberation and consensus, making it much harder to enter into treaties that didn't have widespread support across the country.
High-Stakes Failures and Successes
This high bar has had monumental consequences. The most famous rejection was the Treaty of Versailles after World War I. President Woodrow Wilson, who negotiated the treaty and championed its creation of the League of Nations, failed to get the necessary 67 votes in the Senate. Despite multiple votes in 1919 and 1920, opposition led by Senator Henry Cabot Lodge and Wilson's refusal to compromise doomed the treaty. The U.S. never joined the League, a fact many historians believe weakened the organization and contributed to the instability that led to World War II. More recently, the Comprehensive Nuclear-Test-Ban Treaty was rejected in 1999 with a 48-51 vote, far short of the 67 needed. However, many other major treaties have successfully passed, including the treaty for the Louisiana Purchase, the agreement ending the War of 1812, and the New START treaty limiting nuclear arms with Russia in 2010. These successes show that when a consensus exists, the system works as intended.
The Modern Workaround: Executive Agreements
In the face of this difficult process, modern presidents of both parties have increasingly turned to a different tool: the executive agreement. These are international pacts made by the president that do not require the Senate's two-thirds approval. While they are considered binding under international law, they don't have the same domestic legal status as a treaty and can often be undone more easily by a subsequent president. Famous examples include the North American Free Trade Agreement (NAFTA), which was passed as a 'congressional-executive agreement' with a simple majority in both the House and Senate, and the Iran nuclear deal (JCPOA), which was structured as a political commitment rather than a formal treaty. This shift highlights the ongoing tension between the president's need for diplomatic flexibility and the Senate's powerful constitutional role as a check on foreign commitments.
