But Trump has threatened that strategy with a bristling insular message that has demonstrated a powerful appeal for blue-collar Republicans across religious boundaries.

Trump’s strength among working-class evangelical Christians is helping him to closely press Cruz in Iowa, a state whose Republican caucus has usually favored the candidate that evangelicals prefer. The same dynamic could threaten Cruz in the Southern states that he is counting on to boost his candidacy in early March. Continued Trump strength among blue-collar evangelicals would also frame Midwestern states with many of those voters, including Ohio, Missouri, and Wisconsin, as potentially pivotal showdowns between the two men.

A wild card is whether a third candidate can consolidate the voters at the opposite end of the GOP’s class and cultural spectrum: college graduates who are not evangelical Christians. Those voters provided the foundation for the nomination victories of Mitt Romney in 2012 and John McCain in 2008. But they remain fragmented so far in this race and have not coalesced around a single champion.

Cumulative exit polls that measured results from all the major contests in the 2008 and 2012 Republican nominating contests found that GOP voters in both years divided almost exactly in half between those with and without a four-year college education. Evangelical Christians constituted just under half of all GOP primary voters in 2008 and just over half in 2012. (The difference is probably explained by the fact that the 2012 race ran more heavily through Southern states before Rick Santorum, the runner-up to Romney, conceded in early April 2012.)

Both in 2008 and 2012, there was no major difference in the voting choices of blue- and white-collar evangelical Christians across the key states, according to previously unpublished results from the exit polls in those years provided by Edison Research, which conducts the surveys. The bigger divide was between voters who were and were not evangelical: Romney, for instance, won about half of the former, but just under one-third of the latter, according to a cumulative analysis of 2012 exit polls conducted by ABC Pollster Gary Langer.

But this year, the particular strengths of Trump and Cruz—and the vacuum in the white-collar lane that Romney filled last time—have produced a more complex mosaic.

To understand how states may fall between this field of candidates, it’s revealing to look at education and religious affiliation together to create a four-way grid of Republican voters: evangelicals with and without a four-year college degree, and non-evangelicals with and without such advanced education.

The Education Divide

These four groups may be comparable in size. The NBC/Wall Street Journal Poll tracks conservative Christians through a series of questions that identify so-called “values voters.” When their November and December national surveys were combined to produce a more representative sample, the results showed that college-educated values voters could account for about one-fifth of the GOP primary electorate this year, while the other three groups may each provide about one-fourth.

Janie Boschma

When the electorate is viewed through this lens, Trump consistently polls best among the non-evangelicals without a college degree—the working-class whites many would describe as the prototypical Reagan Democrats.