When a presidential candidate builds momentum by catering to the poorly educated, xenophobic, and possibly blood-thirsty members of the American electorate, the numbers are eventually going to reveal themselves. Here's some data to chew on: According to exit polling data reported by the New York Times, 16 percent of people who voted for Donald Trump in the South Carolina primary, helping him win by a landslide, qualify as white supremacists.
Not necessarily white supremacists in that they're white-hood-wearing members of the KKK, but they were totally fine with telling a pollster from Public Policy Polling—an organization known to lean liberally—that they agreed with the statement that whites are the superior race. Voters who agreed with that statement made up a larger portion of Trump's supporters than any other candidate.
"The P.P.P. poll asked voters if they thought whites were a superior race. Most Republican primary voters in South Carolina — 78 percent — disagreed with this idea (10 percent agreed and 11 percent weren’t sure). But among Mr. Trump’s supporters, only 69 percent disagreed. Mr. Carson’s voters were the most opposed to the notion (99 percent), followed by Mr. Kasich and Mr. Cruz’s supporters at 92 and 89 percent. Mr. Rubio’s backers were close to the average level of disagreement (76 percent)."
If you look at the full data posted by PPP, you'll find that 14 percent of Trump supporters weren't sure that whites are the superior race, as opposed to 16 percent of Trump supporters who were sure. No other Republican candidate achieved double-digit certainty for that question. Marco Rubio came the closest, with nine percent.
CORRECTION: A previous version of this post indicated that 31 percent of Trump supporters believed that whites are a superior race. Sixty-nine percent of Trump supporters indicated that whites are not a superior race; 14 percent weren't sure; and 16 percent found that yes, whites are a superior race.