"I don't believe an X can be elected President."
via the Economist
Americans waaaaaay overestimate voters' prejudices against women and minorities.
Basically, for the red and blue dots, Rs and Ds were asked "Would America vote for a Presidential candidate who is X?" For the grey dots, everyone was asked "Would you vote for a candidate who was X?" Both sides are prone to believe other people will not support the minority identity.
Democrats are particularly prone to this – which ironically makes them less likely to support female or minority candidates due to concerns about electability.
Basically stated, we hate each other more than we hate people of identities, which is not very much, despite us believing that we do.