The Veto Process
When a bill is passed by both the House and Senate, it is sent to the president for his signature. All bills and joint resolutions, except those proposing amendments to the Constitution, must be signed by the president before they become law. Amendments to the Constitution, which require a two-thirds vote of approval in each chamber, are sent directly to the states for ratification. When presented with legislation passed by both houses of Congress, the president is constitutionally required to act on it in one of four ways: sign it into law within the 10-day period prescribed in the Constitution, issue a regular veto, let the bill become law without his signature or issue a "pocket" veto.
When Congress is in session, the president may, within the 10-day period, exercise a regular veto by sending the unsigned bill back to the chamber of Congress from which it originated along with a veto message stating his reasons for rejecting it. Currently, the president must veto the bill in its entirety. He may not veto individual provisions of the bill while approving others. Rejecting individual provisions of a bill is called a "line-item" veto. In 1996, Congress passed a law granting President Clinton the power to issue line-item vetoes, only to have the Supreme Court declare it unconstitutional in 1998.
Bill becomes law without president's signature
When Congress is not adjourned, and the president fails to either sign or veto a bill sent to him by the end of the 10-day period, it becomes law without his signature.
The pocket veto
When Congress is adjourned, the president can reject a bill by simply refusing to sign it. This action is known as a "pocket veto," coming from the analogy of the president simply putting the bill in his pocket and forgetting about it. Unlike a regular veto, Congress has neither the opportunity or constitutional authority to override a pocket veto.
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.