The United States Electoral College is the group of presidential electors required by the Constitution to form every four years for the sole purpose of electing the president and vice president. Each state appoints electors according to its legislature, equal in number to its congressional delegation (senators and representatives). Federal office holders cannot be electors. Of the current 538 electors, an absolute majority of 270 or more electoral votes is required to elect the president and vice president. If no candidate achieves an absolute majority there, a contingent election is held by the United States House of Representatives to elect the president, and by the United States Senate to elect the vice president.