Josh Putnam

If none of the candidates come away from primary season the requisite 1,237 delegates to clinch the nomination, they could face a contested convention, which hasn't happened since 1976.

Josh Putnam, an assistant professor at Davidson College who studies presidential primaries and writes the blog FrontloadingHQ, discusses how states are deciding when to schedule presidential primaries and party caucuses, and how the schedule determines the candidates who get into the race.