Here's the fundamental problem for Democrats next time around.
Obama can't run again. And a Hillary or JoeBi electorate will look nothing like the one that rose up around the President.
Candidate quality matters. A lot. It drives turnout. When that doesn't happen, motivated issue voters (even single issue voters) start to make more of a difference. It's why midterm elections generally look way different than Presidential ones. Democrats got their clocks cleaned with Clinton in office during midterms. But the people still reelected Clinton, because the other guy (although a nice guy) wasn't a good candidate. At least not in today's media-driven age.
In 2016, everything pretty much starts all over again. Anyone making declarations about what happens afterwards is kidding themselves.