So, blacks should go back to their 57% norm. And the Republican share of the black vote should dramitacally increase. I think Republicans will win at least 15% of the black vote.
Actually, I think that's completely unrealistic. Once a person has voted twice, they tend to vote frequently for life. The net impact of Obama has probably been to turn millions of black, and to a lesser extent, Hispanic unlikely voters into likely voters going forward. Note that black turnout largely held in 2010 and 2014. What changed was the margin, which went back to 90/10 for generic Dem from 95/5 for Obama.
Expecting anything in 2016 other than a more diverse electorate than 2012 (72% white) is nothing but Republican wishful thinking. However, Republicans getting 63-65% of the white vote and 10-15% of the black vote may be more than just wishful thinking based on recent polling trends.
What do we get when we keep black and white turnout equal and give the Republican 64% of the white vote, 11% of the black vote and 30% of the Hispanic vote?
We get this, which is basically reverse 2012 with a weird IA/WI split:
