To win, Trump needs to get non-college grads to the polls. Here’s why that will be hard.

That gap wasn’t very wide in the 1950s and 1960s. In 1968, for example, 73 percent of college grads reported voting while 66 percent of high school grads did. By the 1980s, the gap had grown to more than 20 percentage points. In 2012 turnout rates were 73 percent for college grads and 52 percent for those with only high school degrees.

The widening gap appears to be due mostly to declining turnout among high school graduates. Those who’ve gone to college but haven’t graduated vote at lower rates than do college grads — but their turnout hasn’t declined as sharply as those who’ve gone no further than high school. And the educational gap is even wider in midterm elections than in presidential elections.

Research shows that political opinions differ a lot depending on how far people have gone in school. While the proportion of U.S. citizens who are college graduates has increased over that time, they’re still only about a third of the population. Which means that politicians are disproportionately hearing from, and elected by, people with college degrees – who do not represent the country.