Final answer:
To override a presidential veto, two-thirds of both the House and the Senate must vote to pass the bill, providing a check and balance in the legislative process.
Step-by-step explanation:
To override a presidential veto, a two-thirds majority vote is required in both the House of Representatives and the Senate. If a president vetoes a bill, Congress has the power to enact the bill into law despite the veto if both chambers can achieve this supermajority vote. It is an important check and balance within the United States government's legislative process to ensure that no single branch holds excessive power.