Job losses in this recession vs others (note, Obama takes office 14 months after peak employment)
GDP since 1994
And to answer the original question, Democrats simply want a viable and robust middle-class. What this means for them is giving people opportunities to join the middle class, as well as sticking up for people's interests instead of corporate interests.
I find all the talk about "middle class" disingenuous though, since somehow nowadays it's unfashionable to say you're looking out for the poor. So "middle class" is indeed coded language. For all the Democrats failings though, I'd say they look out for the "middle class" much more than the Republicans, who are much more inclined to let corporations trample over people's quality of life.