Some thoughts:
CA: Berkeley
CO: Boulder
IL: Evanston
IA: Iowa City
KS: Lawrence
MD: Takoma Park
MA: Cambridge
MI: Ann Arbor
NJ: Princeton
NY: Williamsburg in Brooklyn
OR: Portland
TX: Austin
VT: Brattleboro
VA: Arlington
WA: Seattle
WI: Madison
How accurate is this? And what would it be for other states?
Williamsburg contains quite a lot of *extremely* Trump precincts in South Williamsburg (some over 90% Trump) so that won't the answer for New York. The answer for New York is probably something like the West Village in Manhattan or Prospect Heights in Brooklyn.
I think my vote would go to Bushwick.
Not nearly enough white people in Bushwick to top this list. We'll see with the 2020 Census figures, but it will still be at least majority Hispanic.
Park Slope is the obvious answer in NYC that no one seems to have mentioned yet and was definitely the right answer a decade ago. Other surrounding neighborhoods are similar and a little younger and are becoming whiter and might have surpassed it: Prospect Heights, Fort Greene, Clinton Hill.
Though some college town Upstate could potentially beat them.