I don't vote for liberal democrats. Never have. Never will. That's how I based my vote. Seriously.
Of course "issues" have something to do with it, but the overriding "issue" was that the Republicans had held Congress for 12 years and the presidency for 8 years, and that frequently means a party change. The pendulum swings both ways. I know for democrats it's probably really exciting right now to imagine that this is the beginning of a democrat ascension that will last for decades or something, but in 4 or 8 years people will be looking for something different. They always do. And that's a good thing. One party governance only leads to corruption, greed, and inertia in preservation of the status quo — no matter the party.