There's something to be said for the politician who recognizes his time is over. His term of office is complete or the public has decided to go another way. I don't think Democrats consider this to be true. There's something to be said for stepping from power with grace and class but I don't think that message got threw to many on the left.
Jimmy Carter was a thorn in GWB's side and in the process has shown himself to be a classless fool. Al Gore is Jimmy Carter times ten. Bill Clinton has been taken in by the Bush family as a friend but that hasn't stopped him from criticizing Bush Jr on a regular basis. Former President Clinton surprisingly has shown more class than Carter and Gore combined even though he seems to be an active part of the current administration.
Contrast them with the way Reagan handled his retirement, or George H. W. Bush, or even George W. Bush. You never hear much about them or even Reagan when he was alive. You hear more of Reagan now that he's gone than you did before Alzheimer's took his memory from him. Romney hasn't been seen speaking in front of a camera since he lost the election.
Part of any great man's legacy is how he conducts himself once he leaves power. Once Obama finally leaves the White House I don't want to ever see his ugly mug ever again, but I'm afraid because he's an attention freak we'll never be rid of him. Why is this the case with Democrats and not Republicans? Why aren't Democrats more like George Washington, who retired to his home at Mount Vernon? Once he left office he left politics for good. Why can't they show some class and just leave?
To be honest, I believe the left feels politics is more important than the nation itself.