It is probably going to be impossible to accurately find out how people are racists via polling. It is unlikely people will honestly answers the question “are you a racist?” You can though tries to use certain polling question to get a rough estimate of how many people still have significant racial hung ups, like the Gallup question on mixed race marriages.
It found 13 percent of non-Hispanic whites are still willing to actually admit to a pollsters that they don’t approve of marriages between blacks and whites. From Gallup:
Polling on this question has improved dramatically over the past decade, but 13 percent still translates to millions of people. This is still a significant voting block when you also consider it is mostly older whites who feel this way and older whites tend to have some of the highest turnout rates of any demographic group.
The effectiveness of racial code words and images has thankfully become a far less common and effective political tool in America but they can still be a factor.