With Americans being so anti-establishment this presidential election cycle and the establishment not wanting to give up power, I could see Donald Trump or Bernie Sanders winning the most pledge delegates but somehow losing the nomination through super-delegates or a brokered convention. Has this ever happened in the past and how did it turn out for that candidate?
The last time that happened was when Estes Kefauver won 13 of the 16 Democratic party primaries in 1952. 32 states, including the large states of Michigan and New York, did not hold primaries in 1952. The delegates for the national party convention in those states were chosen by State Democratic party conventions, before the national Democratic party convention.
Estes Kefauver made a name for himself in the early 1950s, by chairing the Senate Committee on graft and corruption. He also investigated Mafia influence in the politics of big cities in the United States. These investigations hit to close to home for the power brokers in the Democratic party. They flat out refused to support Estes Kefauver and chose to support Adlai Stevenson, who was also backed by Harry Truman. Alben Barkley was Truman's vice-president, but he was 74 years old in 1952 and did not choose to run for the Democratic party nomination.
Source: "Adlai Stevenson: His Life and Legacy" by Porter McKeever (1989)