The Dems lost in 2000 because Clinton triangulated. He signed onto NAFTA and approved a bill to overturn Glass-Steagall. Clinton thereby pissed off enough progressives to throw the election to Bush.
The Dems lost in 2010 because Obama’s turn to the right empowered the GOP and disillusioned Independents and the Democratic base.
If they lose in 2012, the lesson will be clear: Dems lose when they betray progressives and progressive values. That, at least, is the spin we need to spin.