I wouldn't count on the Democrats screwing it up.  The Democrats seem to be bad at winning elections and OK at governing.  The Republicans seem to be good at winning elections, but unable to govern.

I expect, sadly, that there will be some event that gets the Democrats all wound up and manages to alienate the moderates again.  It will probably have to do with gun control, abortion, or gay rights, or some other wedge issue, where the Democrats will get all wound up and propose some legislation that pushes many away, yet again.