The Short Answer: Plurality, Not Majority
No, Missouri does not require a candidate to win a majority (more than 50%) of the vote to secure a federal office like U.S. Senator or Representative. Instead, Missouri operates on a 'plurality' or 'first-past-the-post' system. This is the most common method used in the United States for federal and state elections. All a candidate needs is to get more votes than any other competitor. For example, if Candidate A gets 48% of the vote, Candidate B gets 45%, and an independent candidate gets 7%, Candidate A wins the election despite not having the support of the majority of voters.
An American Standard, Not a Missouri Quirk
While it might seem counterintuitive, Missouri's plurality system isn't unusual. In fact, it's the standard for congressional elections in most of the country. The primary
reason for its widespread use is simplicity and decisiveness; it avoids the cost and lower turnout associated with runoff elections. The system ensures a winner is declared quickly based on a straightforward count. Only a handful of states have different rules. For instance, Georgia and Louisiana require a candidate to achieve a majority in general elections for federal office, triggering a runoff between the top two finishers if no one breaks the 50% threshold.
The 'Spoiler Effect' in Action
The most significant consequence of a plurality system is the potential for the 'spoiler effect'. This happens when an independent or third-party candidate draws votes away from a major-party candidate they are ideologically similar to. This can 'spoil' the election for that major-party candidate, allowing another one to win with less than a majority. For example, a progressive independent might pull votes from the Democratic nominee, inadvertently helping the Republican candidate win, or a libertarian candidate could siphon votes from the Republican, aiding the Democrat. This dynamic often leads to strategic voting, where citizens vote not for their favorite candidate, but for the major-party candidate most likely to defeat the one they like the least.
What About Changing the System?
In recent years, alternatives like ranked-choice voting (RCV) have gained traction in other parts of the U.S. as a way to eliminate the spoiler effect and ensure winners have broader support. Under RCV, voters rank candidates in order of preference. If no candidate has a majority of first-preference votes, the last-place candidate is eliminated, and their voters' second choices are distributed, a process that continues until one candidate secures over 50%. However, Missouri has moved in the opposite direction. A 2022 initiative to bring top-four primaries and ranked-choice voting to the state did not make the ballot. Furthermore, in 2024, voters approved a constitutional amendment that explicitly prohibits ranked-choice voting in the state, cementing the plurality system.
The Only Exception: A Tie
There is one scenario where getting the most votes isn't quite enough: a perfect tie. According to Missouri state law, if two or more candidates for a federal office receive an equal and highest number of votes, the governor must issue a proclamation ordering a special election to break the tie. While exceedingly rare in races with hundreds of thousands or even millions of votes, it remains the only exception to the first-past-the-post rule. For statewide offices like governor, a tie is decided by a joint vote of the state legislature.
