So yes, white people are still the base of the democratic party. Bernie actually did pretty poorly with some white people he should have been able to win (midwestern & appalachian-besides WV- whites).
There was really no excuse for Bernie to lose Missouri, Kentucky, Ohio, and Pennsylvania. Hell, he even could have kept Tennessee closer. There were swaths of white voters who he didn't appeal to so I'm not sure why that other poster went out of his way to declare POC were not the base... ok, and Bernie didn't appeal to enough white people either lol
No Democrat is going to win the presidency without winning the votes of minorities by large margins. Without minorities Democrats wouldn't even have a chance at winning several swing states (if you remove large diverse cities from purple states they will turn red).
The black, Latino, and young Obama '12 non-voters were more consequential than the "Obama -> Trump WWC voter" who supposedly would have voted for Bernie if he were on the ballot. Hopefully Senator Sanders can evolve in his rhetoric on how the Democratic Party should galvanize voters moving forward. I have been very turned off by some of his assertions. I have seen him turn the corner a bit on that, so thankfully someone has gotten in his ear.