One chart is all you need.  From NBC’s 2012 exit polls:

Bolding and coloring mine.  You see those percentages? In 2012 black voters made up 13% of the electorate, same as in 2008; and the GOP got half as many voters* from that demographic in 2012 as we did in 2004 and 2000 (when black voters made up a few points less of the total electorate). There are two things that we know about the next election, more or less: first, the Democrats [are] tanking among white voters.  Second, black voters aren’t going to come out for a non-black Presidential candidate with the same intensity that they did for Barack Obama. Add those two together, and the end result looks very bad for the Democratic party.

And that’s why Hillary Clinton is still being propped up by the Democratic establishment: she’s the most prominent female politician that they have right now. I personally don’t think that she’s going to be able to recreate Barack Obama’s 2012 performance when it comes to white women voters, but former Secretary Clinton has a better shot at it than pretty much anybody else. …And that is, as they say, pretty much it.

Moe Lane (crosspost)

*Mind you, this means the difference between ‘barely double-digits’ and ‘middle single-digits.’