The Washington Post's Dana Milbank writes that Trump supporters are modestly more racist than those of Kasich and Cruz. He makes much of this modest difference. I'd interpret it differently.
The Donald has repeatedly criticized politically correct speech, defined as saying not what you mean but what you know is widely acceptable, what you are "supposed to say." My guess: Trump's white supporters are no more racist than other whites. However, echoing their champion, they refuse to say they brook no racist feelings or resentments.
Those who really hate feeling compelled to say things they neither believe nor favor in order to be socially acceptable logically gravitate to Trump. He has derided the idiocy of political correctness. Expect his followers to do less self-editing for social desirability,
