What is required for Congress to override a presidential veto?

To override a presidential veto, Congress must achieve a two-thirds majority in both the House of Representatives and the Senate. This high threshold reflects the intention of the framers of the Constitution to ensure that a significant consensus is required to counteract the President's decision to reject legislation. By requiring a two-thirds majority, the system balances the powers of the executive and legislative branches, making it clear that overriding a veto is a significant legislative action that should reflect broad support among lawmakers.

The other options do not meet the constitutional requirements for overriding a veto. A simple majority would not be sufficient, as it does not reflect the necessary level of agreement needed to counter the President's authority. A unanimous vote is unrealistic and not required by the Constitution. Lastly, a three-fifths majority applies specifically to certain parliamentary procedures, such as cloture in the Senate, and is not relevant in the context of overriding a veto. Therefore, the correct answer highlights the importance of achieving a substantial consensus within Congress.