The win spells probable doom for Cruz, whose campaign, staked on a strategy of winning over evangelical voters, fell flat in its first real test. Born-again Christians, who Cruz predicted would turn out in droves to propel him to victory, instead broke decisively for Trump, 33 percent to Cruz's 27 percent.
That's a coup for a larger-than-life candidate whose blustery rhetoric on immigration and terrorism seemed to make up for his apparent lack of religious credentials with these voters. It was perhaps the most important demographic victory for Trump, but certainly not the only one.
Instead, exit polls from the Washington Post tell a larger story about how Trump has molded the views of Republican voters — and turned them in his favor with wild success.
All this should alarm party elites set on stopping Trump from sweeping the nomination. South Carolina's population looks a lot like those of the seven southern states voting on March 1, and unless there is a major shift in the race, the advantages Trump has built himself will likely hold up.
Republicans really want a Muslim ban
Take Trump's proposed blanket ban on Muslims entering the US. Once considered an extreme proposition of questionable constitutionality, the idea won over 74 percent of Republican primary voters — whether or not they ultimately even voted for Trump.
In fact, only about 41 percent of Muslim ban supporters actually picked Trump; a solid 20 percent broke for Rubio. Of course, after Trump began trumpeting his anti-Muslim views, Rubio countered with what my colleague Matthew Yglesias argued is an even more radical plan, to shut down any meeting place (including coffee shops) where Muslims might gather.
Still, the lopsided margin of voters who favor the idea should drive home how thoroughly Donald Trump has implanted himself in the minds of voters, so that even if he doesn't ultimately become the party's nominee (which, it must be said, he very well might become), his ideas will continue to shape the race.
Republican voters like Trump's message of fear
More broadly, Trump's two main focuses, immigrants and terrorists, have captured the minds of Republican voters. Fully 31 percent of voters rated terrorism the top issue in the race, with an additional 10 percent rating immigration as a top concern. Among both groups, Trump wins handily. The advantage is particularly stark among voters citing immigration — 51 percent of those voters pick Trump, compared with 25 percent for Cruz and 11 percent for Rubio.
In the same vein, 44 percent of the electorate thinks "most illegal immigrants" should be deported — a clear echo of the unusually harsh tactics Trump has said he would use to purge America of more than 11 million unauthorized immigrants. Among those voters, 47 percent cast ballots for Trump, compared with 24 percent for an equally adamant Ted Cruz and 15 percent for Rubio.
Republican voters really want an outsider as their nominee
Trump is not the only candidate to play the party outsider game — and it's not an entirely new trope in Republican politics. But his strategy of broadcasting his lack of experience in public office seems to have undercut even Ted Cruz, who champions his status as the single most loathed member of the US Senate.
Cruz doesn't register as outsider enough for Republican voters, 48 percent of whom said they prioritized voting for someone who is "outside the establishment." Of those voters, 69 percent voted for Trump; only 13 percent voted for Cruz.
Moreover, most Republicans in the state seemed unaffected by the endorsement of their governor, Nikki Haley, who sided with Rubio in the days leading up to the primary. Once a true bellwether of party support, the governor's endorsement didn't matter to fully 72 percent of Republicans this primary season. And of those who said they didn't care about Haley's endorsement, Trump had a 22-point advantage over Rubio.
Trump doesn't have any major demographic problems
Looking at the age, sex, and educational breakdown of Trump voters, it seems that the candidate doesn't have any one outstanding gap in support.
Take his stronghold of voters with only a high school diploma. This demographic has long been called Trump's base, and sure enough, fully 45 percent of those voters sided with Trump, compared with 27 percent for Cruz and 16 percent for Rubio.
But college-educated Republicans — who, at 33 percent, make up a larger share of the electorate than voters with high school diplomas — still broke for Trump, if less decisively. He won 29 percent of those voters, compared with Rubio's 24 percent.
Age doesn't seem to be a major barrier, either. Though Trump won older Republicans handily — attracting 36 percent of voters ages 45 to 64 — he didn't exactly fall behind among younger voters, either. Among the two youngest demographics polled, he ran about even with both Cruz and Rubio.
Men and women both also voted for Trump most often, though a larger percentage of men (36 percent) than women (29 percent) voted for him. Women make up a smaller proportion of the Republican electorate than men do, which further neutralizes Trump's slight gender deficit.