Overall black vote in 04 was 11% (which amazingly Bush got
11% of), white vote was 77%, hispanic was 8%.
http://www.cnn.com/ELECTION/2004/pages/results/states/US/P/00/epolls.0.html
2008 the numbers were 13% black, 74% white, hispanic 9%.
http://www.cnn.com/ELECTION/2008/results/polls/#USP00p1
2012 the number was 13% black, 72% white, 10% hispanic. Surprisingly the black GOP vote actually went
up from 5% to 7%.
http://www.cnn.com/election/2012/results/race/president#exit-polls
Now let's just say the GOP doesn't repeat Bush's 11% vote among the black electorate, obviously they can increase the vote among whites, increase the vote among hispanics, or hope (or encourage) blacks to stay home. That last one with no Obama on the ballot is a definite possibility.
I'm also not so sure the Clintons tap that full extent of the 95-93% of the black vote that Obama was getting, much less the 13% turnout level the last two elections.
I'm not saying the GOP wins (oh no), I'm just saying this country is divided 50/50 still and
if you think the Clintons will be exciting people or driving black or hispanic turnout all on their lonesome, well, I wouldn't be so sure of that.