Twenty-second Amendment to the United States Constitution
The amendment prohibits any individual who has been elected president twice from being elected again. Under the amendment, an individual who fills an unexpired presidential term lasting greater than two years is also prohibited from winning election as president more than once. Scholars debate whether the amendment prohibits affected individuals from succeeding to the presidency under any circumstances or whether it only applies to presidential elections.
List of Democratic Party presidential primaries
Democratic incumbent President Barack Obama ran for re-election, and faced no major opposition in the primaries. Minor opposition candidates won 40+% of the vote in four state primaries -- including Keith Judd, a convicted felon, who was still serving a federal prison sentence when he placed second in West Virginia. However, the delegates won by the opposition were forbidden from attending the Democratic convention in Charlotte.