A brokered convention occurs when there are not enough delegates “won” during the presidential primaries for a single candidate to have a majority during the first official vote at a party’s nominating convention. The nomination is then decided though political deals between candidates, party bosses and subsequent votes until one candidate receives a majority.
Before the era of presidential primaries, political party conventions were routinely brokered. The most recent brokered convention nominees were Adlai Stevenson at the 1952 Democratic convention and Thomas Dewey at the 1948 Republican convention.
More recently, a brokered convention is mostly just a political junkie’s fantasy. The modern party primary system almost always determines an overwhelming winner of delegates. And as David Frum notes, it’s hard to imagine a “brokered convention” when there is no such thing as political “brokers” any more. Elected delegates to a convention aren’t going to be swayed by political leaders deciding the nominee in a backroom.
A brokered convention was portrayed in the film The Best Man starring Henry Fonda.