(Mark Hirsch/Getty Images)

At a polling location at an Iowa State University apartment complex, a long line snaked down a hallway and around and back up on Tuesday evening. Those in line expected it would take at least two hours to reach a ballot.

One woman left without voting, saying the line was too long. "This voter suppression," one man angrily said.

Many of those in line were college students and many planned to register that day, a process that can take more time.

Many Iowans have already voted. As of the end of the day on Monday, 673,124 Iowans had cast their ballots, a nearly 25 percent increase from the 2008 election. Final turnout for that election was around 1.5 million.