A whip is an official in a political party whose primary purpose is to ensure party discipline in a legislature. Whips are a party’s “enforcers”, who typically offer inducements and threaten punishments for party members to ensure that they vote according to the official party policy. A whip’s role is also to ensure that the elected representatives of their party are in attendance when important votes are taken.
In the United States there are legislatures at the local (city councils, town councils, county boards, etc.), state, and federal levels. The federal legislature (Congress), the legislatures in all states except for Nebraska, and many county and city legislative bodies are divided along party lines and have whips, as well as majority and minority leaders. Similarly, the whip may also be known as the assistant majority or assistant minority leader.
Both houses of Congress, the House of Representatives and Senate, have majority and minority whips. They in turn have subordinate “regional” whips. While members of Congress often vote along party lines, the influence of the whip is weaker than in the UK system. One reason is that a considerable amount of money is raised by individual candidates, and members of Congress, or any other person, cannot be expelled from a political party, which are formed simply by open registration. In addition, because preselection of candidates for office is generally done through a primary election open to a wide number of voters, a candidate who obeys their constituents’ rejection of the party line cannot easily be deselected by his party.