Some U.S. states and municipalities require that the winning candidate in an election must poll at least 50% of the vote. But if three or more candidates run for a single office it is possible that no single candidate will win the required majority. Then a second election is required between the top two vote-getters to determine a majority winner. The runoff election is typically held from two to four weeks after the first election.

The rationale behind this "majority clause" is three-fold: 1) Majority Rule. The basic principle of majority rule demands that an elected representative should have the support of more than 50% of the voters. 2) Legislative Mandate. Candidates elected with less than 50% of the vote may have difficulty acting with strength in the government. They may be perceived as weak and illegitimate because more people voted against them than voted for them. A candidate who wins with only 30% of the vote may have difficulty demanding action in the legislature because more people disagreed with her/his views than agreed with them. 3) Preventing "spoilers" and "split votes." In a race where like-minded candidates run for the same position, they may knock other off and cause the "greater evil" candidate to win. To prevent this in a plurality election, many voters will vote for the "lesser of two evils" rather than their favorite candidate.

As noble as the majority requirement may be, however, the use of two round runoff elections is beset by problems. For one, these runoffs are extremely costly for taxpayers and election administrators who must pay for the administering of the second election. Runoffs are also costly for the candidates who must raise funds for two elections instead of one, thereby undermining one of the goals of campaign finance reform. Furthermore voter turnout tends to decrease in the second (runoff) election, once again undermining majority rule.

Fortunately, there is a better way. Instant Runoff Voting (IRV) is gaining attention as a better solution to the problems of plurality elections. IRV allow voters to cast a vote for their runoff choice at the same time they cast their vote for their favorite candidate. They do this by ranking candidates in order of choice: first choice, second choice, third choice, etc. The rankings are then used in a series of runoffs to determine a winner with true majority support. It's like holding a two-round runoff, but doing it all with one vote. IRV is best for electing single candidates like a president, governor, mayor or a district representative. It all but eliminates the "lesser of two evils" and "spoiler" problems, since a voter can vote for their favorite candidate knowing that if their first choice doesn't win their vote will transfer to their next ranking. Compared to two-round runoffs, IRV saves candidates and taxpayers the cost of a second election. 

See also IRV