More than three-quarters of Cruz's supporters identified as evangelical Christians, compared with fewer than 6 in 10 of Marco Rubio and Donald Trump supporters. The concentration of evangelical Christians among Cruz backers is similar to the last two Iowa Republican victors, Rick Santorum and Mike Huckabee; these voters made up 76 and 83 percent of their supporters, respectively. Both Trump and Rubio received a greater share of their support from evangelicals than Mitt Romney in 2012 or John McCain in 2008, both of whom lost the state but eventually won the party's nomination.

Ideology was also a sharp dividing line between Cruz's, Trump's and Rubio's supporters. Nearly two-thirds of Cruz supporters said they are "very conservative" in the entrance poll. That compares with only 35 percent of Trump supporters and 26 percent of Rubio backers who were strongly conservative, a result of Cruz's dominant performance with this group.

Cruz's "very conservative" coalition is again most similar to Santorum, who took two-thirds of his vote from this demographic. Huckabee's backers leaned less to the right, with similar shares identifying as "very" and "somewhat" conservative.

And in a somewhat counterintuitive finding -- given a surge in Republican turnout to record-high levels -- Cruz did not rely on these first-time caucus-goers to propel him to victory. Just 37 percent of Cruz's backers said they were attending their first caucus, compared with 43 percent for Rubio and 57 percent for Trump.

Cruz's coalition points to both strengths and challenges in upcoming contests. His victory in Iowa is a major step to coalescing support among evangelical Christians and very conservative Republicans, who make up hefty portions of the GOP electorate across the country. In 2012 primaries where exit polls were conducted, an average of 35 percent said they were "very conservative," while 50 percent identified as evangelical Christians.