Evan Soltas ran the numbers.
In the Illinois primary, voters vote for delegates who have their affiliation displayed. They do not vote directly for the candidates. And there can be more than one delegate for each candidate on the ballot.
Soltas then matched publicly available voting data to publicly available census data to estimate the “whiteness” of each delegate.
Trump delegates won significantly more votes when they had "whiter" last names relative to other delegates in their district. This effect does not appear for any of the other Republican candidates, and it is strongest in districts with high Trump vote shares.
Trump delegates who were likely to be perceived as nonwhite, in particular, won about 2 percentage points less of the vote …
My conclusion from all this is that Trump voters are significantly more racially motivated than Illinois Republicans who did not vote for Trump. Since Donald Trump won Illinois by 8 percentage points, the effect was politically important but not decisive.
I get the most mileage out of this when I think about what happened before Trump came along. I’m quite sure there were always racist voters. But these results are suggesting that they were spread evenly across Republicans. I don’t know of any data about Democrats, but I wouldn’t be surprised if they worked the same way.
So is Trump a magnet for existing racists, or did he help create new ones?