<P> Prior to 1936, nomination for president was required, not merely by a majority, but by two - thirds of the total number of delegates . Unless there was a popular incumbent, something that only happened three times between the Civil War and World War II, getting that many votes on the first ballot was implausible . The choice was an often contentious debate that riled the passions of party leaders . Delegates were forced to vote for a nominee repeatedly until someone could capture a minimum number of delegates needed . In 1912, 1920 and most notoriously in 1924, the voting went on for dozens and dozens of ballots . </P> <P> Backroom deals by party bosses were normal and often resulted in compromise nominees that became known as dark horse candidates . Dark horse candidates were people who never imagined they would run for president until the last moments of the convention . Dark horse candidates were chosen in order to break deadlocks between more popular and powerful prospective nominees that blocked each other from gaining enough delegates to be nominated . One of the most famous dark horse candidates nominated at a Democratic National Convention was James K. Polk, who was chosen to become the candidate for president only after being added to the eighth and ninth delegate ballot . </P> <P> The rules were changed to a simple majority in 1936 . Since then only one multi-ballot convention (1952's) has taken place . </P> <P> Before about 1970, the party's choice of the vice-presidential nominee was usually not known until the last evening of the convention . This was because the presidential nominee had little to do with the process and in many cases was not known at the start of the convention . In 1944 and 1956, the nominee let the convention choose the running mate without a recommendation, leading to multiballot voting, and other times, successful attempts to sabotage the nominee by scattering delegate votes for someone else besides his choice, as in 1972 and 1980, led to disruptions . </P>

Who selects the delegates that attended the national conventions