The “diploma divide” among Republican voters was a key factor in the 2012 primary, and it has recurred in 2016. In 2012, college-educated Republicans lined up behind Romney, while those without degrees fragmented among several candidates. But in 2016, as David Wasserman noted in December, it is college-educated Republicans who have divided their support while those without degrees have coalesced behind Trump. Consequently, Trump leads the GOP field because even though he gets only a quarter of Republicans who graduated from college, he gets two-fifths of those who didn’t.

The problem for Trump (or any candidate) is that winning non-college graduates while losing degree holders does not a winning coalition make. All it does is guarantee defeat. Per the 2012 exit polls, Romney won college graduates 51 to 47 percent over President Obama. It was the only educational cohort Romney won on his way to a four-point loss.

Trump supporters might counter that he would make up for it by winning overwhelming support from working-class voters. This is wrong for two reasons. The first reason is that, as seen in the Quinnipiac poll, Trump only breaks even with non-college graduates in the general election. The second reason is that there simply aren’t enough working-class voters to make up for the catastrophic losses among college-educated voters Trump is destined to incur.

Voting propensity is strongly correlated with educational attainment. The more educated one is, the more likely one is to vote. Unsurprisingly, therefore, the two most reliable voting groups in the United States are voters with bachelor’s degrees and those with post-graduate degrees.