How Congress responds to a veto
When the President returns a bill to the chamber of Congress from which it came, along with his objections in the form of a veto message, that chamber is constitutionally required to "reconsider" the bill. The Constitution is silent, however, on the meaning of "reconsideration." According to the Congressional Research Service, procedure and tradition govern the treatment of vetoed bills. "On receipt of the vetoed bill, the President's veto message is read into the journal of the receiving house. After entering the message into the journal, the House of Representatives or the Senate complies with the constitutional requirement to 'reconsider' by laying the measure on the table (essentially stopping further action on it), referring the bill to committee, postponing consideration to a certain day, or immediately voting on reconsideration (vote on override)."
Overriding a veto
Action by both the House and the Senate is required to override a presidential veto. A two-thirds majority vote of the Members present is required to override a presidential veto. If one house fails to override a veto, the other house does not attempt to override, even if the votes are present to succeed. The House and Senate may attempt to override a veto anytime during the Congress in which the veto is issued. Should both houses of Congress successfully vote to override a presidential veto, the bill becomes law. According the the Congressional Research service, from 1789 through 2004, only 106 of 1,484 regular presidential vetoes were overridden by Congress.