Final answer:
A president might use an executive-congressional agreement rather than a formal treaty because it is easier to enact (requiring only a simple majority in both the House and Senate), and can be faster to implement. Executive agreements are generally considered legally binding like treaties unless they change federal law. However, they are less durable and can be reversed by subsequent presidents without Senate involvement.
Step-by-step explanation:
Why Might a President Choose to Use an Executive-Congressional Agreement?
Presidents may opt for an executive-congressional agreement over a formal treaty for several reasons. Formal treaties require a two-thirds majority in the Senate for ratification, which can be particularly challenging to obtain. This difficulty is amplified when considering the quick pace and extensive demands of modern foreign policy. An executive-congressional agreement such as the North American Free Trade Agreement (NAFTA) only requires a simple majority in both the House and Senate. Moreover, while executive agreements do not commonly engender controversy, certain agreements, like the Iran Nuclear Agreement, can generate significant debate over whether the agreement should have been a treaty.
Executive agreements are also advantageous as they can be executed more swiftly than treaties and are generally considered legally equivalent to treaties provided they don't alter federal law, as per the U.S. Supreme Court's ruling in United States v. Pink. However, they do come with the downside of being less durable; they can be reversed by subsequent presidents without needing to undergo the same rigorous process that treaties require for their nullification.
One key consideration informing the choice between a treaty and an executive agreement is whether the President aims to bypass a potentially uncooperative Senate—a strategy referred to as the "evasion hypothesis"—or if it is viewed as a more efficient tool for handling a multitude of agreements annually.
A historical example underlining the tension between executive agreements and treaties is President Dwight D. Eisenhower's administration. After using numerous executive agreements, Congress considered a constitutional amendment to change the treaty process, prompting President Eisenhower to revert to using the formal treaty process more frequently.