Article I of the Constitution establishes the legislative process. Bills are introduced in either the Senate or House of Representatives. After passing both chambers with a majority vote of approval, the bill is presented to the president. If the president approves the bill, it becomes law. However, the president, as head of the executive branch, also has the ability to veto the bill. From 1789 to 2013, presidents have vetoed 2,564 bills.

Constitutional Power

Once a bill has passed both chambers of Congress, the Constitution provides the president 10 days, not counting Sundays, to act on the bill. If the president signs the bill, it becomes law. The president may decline to sign the bill, but provided Congress is still in session during that 10-day period, the bill automatically becomes law even without his signature. However, Article I, Section 7 of the Constitution also gives the president the power to veto the bill by returning it to the legislative body where it originated. George Washington exercised the first veto on April 15, 1792. Franklin D. Roosevelt used the presidential veto more than any other president, vetoing 635 bills.

Return to Congress

If the president chooses to veto a piece of legislation, it is returned to the House or Senate where it was first introduced. Usually, the president includes a note with reasons the bill was vetoed. At this point, the congressional body reconsiders the bill in light of the president's objections. The process of reconsideration is governed by House and Senate rules since the Constitution doesn't mandate a procedure for reconsidering a vetoed bill. Neither chamber of Congress has any obligation to attempt to override the presidential veto. However, a vote may be scheduled if congressional leaders believe there are enough members in favor of the bill becoming law.

Congressional Override

The Constitution allows Congress to override a presidential veto if two-thirds of the members of each house vote in favor of passing the bill into law. Congress interprets this as requiring two-thirds from members present at the time of the vote, not two-thirds of the body's total membership. The first congressional override occurred in 1845. Through 2013, Congress has overridden just over 4 percent of all presidential vetoes. During Andrew Johnson's administration, Congress overrode 15 of his 21 vetoes, the most of any president.

The Pocket Veto

If Congress sends the president a bill and adjourns at any point during the 10-day period and the president doesn't sign the bill it does not become law. This is known as the "pocket veto," and it is allowed under the same section of the Constitution that provides the president the power to veto legislation. When Congress adjourns, the president has no way to return the bill. In 1812, James Madison became the first president to use the pocket veto. If the president vetoes legislation using the pocket veto, the only way for Congress to potentially override the veto is to reintroduce the legislation as a new bill in its next session.