Voter turnout is a constant issue in the U.S. around an election, particularly among the young. In exit polls from Tuesday's midterms, for example, only 13 percent of voters were under 30.

Nonvoters are also more racially diverse than the voting population and are less educated. More than 40 percent of likely nonvoters in the 2014 elections identified as Hispanic, black or other racial/ethnic minorities, compared with 22 percent of likely voters. While most voters (72 percent) have completed some college, nonvoters are more likely to have never attended college.

On average, the populations who are likely to avoid the polls are also the populations likely to vote for a Democrat, which presents a challenge for the Democratic Party. The challenge of turning out voters likely factored into the Democratic losses in the midterm elections, when Republicans gained control of the Senate.

Because turnout drops for midterm elections compared to presidential elections, it makes more sense to compare Tuesday's voter turnout to the last midterm elections in 2010. Turnout was less for eligible voters this time around: 36.6 percent voted, compared with 40.9 percent in 2010, according to data from the United States Elections Project.

The differences were especially stark in some states that saw nosedives of crazy proportions. Turnout numbers in Washington, Delaware, Missouri, South Dakota, California and Indiana all dropped by more than 10 percentage points between 2010 and 2014. And although some states made gains in voter turnout (Nebraska, Wisconsin, Louisiana, Maine, to name several), most states dropped. Only 12 states turned out a higher percentage of eligible voters this year than in the last midterms.

