A brokered convention occurs in a US Presidential convention where no nominated candidate has received the needed delegates decided by primary election and caucuses to secure the nomination. If two people running in the primary elections are nearly tied in delegates as the nominating convention approaches, the decision of who will actually run for President is taken out of the hands of the people. Instead, it’s left up to unpledged delegates (called so by the Republican party) or the Democrat Party’s superdelegates.
Superdelegates or unpledged delegates are essentially the same thing. They are important members of the Democrat or Republican Party respectively, who get a vote at their respective conventions. They include former presidents, elected officials, and top members of each party. Usually, superdelegates don’t have much final say in the presidential nomination. From the candidates running for the nomination, a clear winner can emerge long before the convention is held. When candidates come into the convention in a dead heat or a near tie, superdelegate votes are then exceptionally important and will decide who is nominated to run for president.
This is called a brokered convention because it involves much discussion, multiple votes, political trades, and what might be called backroom dealings. Since it is important for a party to appear united before entering a Presidential race, attempts to sway votes in a single direction is valuable. When superdelegate votes split nearly evenly, this can represent a failure for the party to unite behind a single candidate, which may affect the presidential race.
The brokered convention is not a democratic process. In fact many people argue that a brokered convention directly controverts the will of the people. However, since the people have split the vote between two candidates, so that delegates are nearly equal, both parties feel that at this point they have the right to interfere in order to choose the nominee for President. But it cannot be denied that choice does not have to be based on popular vote; it can be based on any number of agreements that do not need to be made public.
The last brokered convention in the US was in 1952, when the Democratic Party nominated Adlai Stevenson, who did not win in the general election. The 1948 brokered convention that resulted in the Republican nomination of Thomas Dewey also did not result in a win for Dewey. Though this can hardly be called a pattern, it suggests that candidates chosen in a brokered convention may not have as good of a chance at winning the election.