After both chambers pass a bill, the President has the last ordinary move. The Constitution gives Congress a way to answer a veto, but a narrow timing rule can put a bill out of reach.
When a bill reaches the President there are three options. Sign it, and it becomes law. Veto it, by returning it to the chamber where it began with a statement of objections. Or do nothing: if Congress is in session, the bill becomes law automatically after 10 days (Sundays excepted) without a signature.
A veto is not the final word. If two-thirds of both the House and the Senate vote to override, the bill becomes law without the President's signature. That two-thirds bar in each chamber is high, so most vetoes are sustained.
The 10-day rule has a twist. If Congress adjourns during that window so the President cannot return the bill, inaction kills it instead of enacting it. This is a 'pocket veto,' and because there is no returned bill for Congress to act on, it cannot be overridden; Congress must start over.
Presentment is the final gate. Everything before it, committee work, floor votes, reconciling the two chambers' versions, only matters once both chambers have agreed on identical text to send to the President.
