Yes. Its been very consistent over the past 10-15 years. 85-95% of blacks vote Democrat and turnout stays roughly the same as white turnout. What they can't count on, however, is Latino turnout (usually horrendous in midterm years and OK at best in presidential years), and enough of the white vote for them to win. Not many people on the left recognize it, but they actually do have a problem with white voters. Especially in the Midwest, the white 'working class' people are increasingly Republican.
I'd add to this that Democrats are reliant in many states on college-aged liberal whites, who don't vote for candidates that don't "excite" them (whatever that means). That kind of dropoff among young voters and Latinos, like you pointed out, is a bigger problem. I imagine (and am broadly stereotyping) that blacks vote consistently due to treasuring the franchise in a different way than other groups do due largely to the historic discrimination and disenfranchisement experienced by that group.
