In the federal Congress, the role of the Majority Leader of the United States House of Representatives and the Majority Leader of the United States Senate differ slightly. In the United States Senate, the majority leader is the chief spokesperson for the majority party, as the president of the Senate is also the Vice-President of the United States, and the President pro tempore, though technically a substitute for the president of the Senate, is in reality a largely ceremonial position (albeit powerful nonetheless, being third in line of succession to the presidency).
In the United States House of Representatives, the majority leader is elected by U.S. Congressmen in the political party holding the largest number of seats in the House. While the responsibilities vary depending upon the political climate, the Majority Leader of the United States House of Representatives typically sets the floor agenda and oversees the committee chairmen.
The majority leader is often assisted in his role by whips, whose job is to enforce party discipline on votes deemed to be crucial by the party leadership and to ensure that members do not vote in a way not approved of by the party. Some votes are deemed to be so crucial as to lead to punitive measures (such as demotion from choice committee assignments) if the party line is violated; decisions such as these are often made by the majority leader in conjunction with other senior party leaders.
In the various states, the majority leader of a state legislative chamber usually performs a similar role to the Majority Leader of the United States House of Representatives. The state senate president pro tempores are typically not ceremonial, but instead are more akin to the Majority Leader of the United States Senate.