Who must approve treaties negotiated by the president?

Treaties negotiated by the president require the approval of the Senate. This is established by the U.S. Constitution, specifically Article II, Section 2, which states that the president has the power to make treaties, but those treaties must be ratified by a two-thirds majority of the Senate. This process ensures a system of checks and balances, as it requires collaboration between the executive and legislative branches of government. The involvement of the Senate in the treaty approval process reflects the intention to engage representatives of the people in significant decisions regarding international agreements.