What fraction of both houses must vote to override a presidential veto?

To override a presidential veto, a two-thirds vote is required in both the House of Representatives and the Senate. This high threshold ensures that there is a significant consensus among lawmakers before they can counteract the president's decision.

The reasoning behind the two-thirds requirement is rooted in the framers' intent to balance power between the executive and legislative branches. By requiring a supermajority, the Constitution emphasizes the need for a substantial agreement across party lines and different chambers, thereby discouraging impulsive decisions that could arise from a simple majority.

In contrast, one-half, three-fourths, and just a majority do not meet the established criteria for overriding a veto, as these fractions do not reflect the level of agreement needed to challenge the president's authority. Thus, the requirement for a two-thirds majority is a fundamental aspect of the checks and balances outlined in the Constitution.