Pollster Dan Cox said on Monday that a cultural gap and demographic shifts play into why the Republican Party struggles to connect with young voters.

"You have two things going on. There's a culture gap between where young people are on a lot of issues, whether it's abortion, reproductive rights issues, whether it's LGBT issues," Cox, research director at the Public Religion Research Institute, told Hill.TV's Joe Concha on "What America's Thinking."

"Then you also have this demographic shift. So every year, young people are getting more or less white. So they're increasingly African-American, Latino, [Asian Pacific Islander], and Republicans don't do well among those groups," he continued.

Millennials, as well as minorities, could play a major role in Tuesday's midterm elections.

An NBC News/GenForward survey released last week found that a third of voters ages 18-34 said they would definitely vote in the midterm elections.

Voters have also increasingly taken advantage of early voting this year, which could also suggest that turnout among minorities and young voters could be high.

At least 31 million has voted as of Monday, according to data compiled by Catalist, which was first reported by CNN.

The data also found that voters under 30 made up a bigger percent of early voters this year than they did during the 2014 midterm elections.

— Julia Manchester