Nate Cohn discounts Stephens-Davidowitz’s research:
Between the well-established anti-liberal trend in the South and the West’s tendency to favor challengers, any liberal Democratic challenger would have been expected to perform best in the states with low racism and struggle in the states with high racism. The performances of the prior three liberal, Democratic challengers is consistent with this hypothesis. Racism probably didn’t cost Kerry the presidency or save George H.W. Bush from an extremely close race with Michael Dukakis, yet that’s basically what the Stephens-Davidowitz’s model would suggest
The Dish 