The danger with Trump is that he falls below Romney #'s with Hispanic and Asian voters. This is what happens with black and white turnout at 65%, Hispanic and Asian turnout at 50% and the Republican getting 63% of the white vote, 10% of the black vote, and 20% of the Hispanic and Asian vote:
The only R pick-up over 2012 is Ohio.
That tool doesn’t work well, hence the weird WI/IA split.
Trump is a white turnout booster, so it won't be surprising if he managed to get more than 67% of white turnout. His share of whites will also be greater than normal for a Republican. I think he can't go below 61% and 63-65% of whites is possible.
I don't think that the Republican share of the Hispanic vote could ever be lower than that what Romney got. They simply hated the guy. In fact, I think there will be a very small rebound, even with Trump as candidate. My estimate is around 30% of the Hispanic vote goes Republican, more if Bush is the nominee.
Asian vote should return to norm for Republicans, which is 40-50%.