Quinnipiac Poll (emphasis mine):

Twenty percent of registered Republican voters said they would vote for Trump in the Republican primary, with 13 percent favoring Wisconsin Gov. Scott Walker (R) and 10 percent choosing former Florida Gov. Jeb Bush (R).

However, Trump also dominated the “no way ” list, with 30 percent of Republican voters saying they would never vote for Trump in the presidential primary, while 15 percent said they would never vote for New Jersey Gov. Chris Christie (R) and 14 percent said they would not vote for Bush. The real estate mogul also has a low favorability rating, with just 27 percent of voters viewing him positively.

You just can’t win if 30% of your own party will “no way” vote for you.