Trump getting the Black Vote in the high teens is very possible and would still be a catastrophe for Democrats. The models for how states and congressional districts vote changes if you do not consider the Obama years of 95+% Dem vote to be the future base line. To a large extent, what we are seeing is a reversion to mean. Think about What those models of congress look like if Republicans can get 15-18% of the black vote like they did when Reagan or Bush was president.