Via Ben Smith, this comment from a Democratic voter to President Obama perfectly encapsulates the liberal mood:

I'm exhausted. Exhausted of defending you, defending your administration, defending the mantle of change that I voted for.

This gets at what I've been writing about a lot, which is liberals' inability to sustain political enthusiasm, especially when their party holds power. Conservatives often find it natural to muster enthusiasm on behalf of a party in power. Liberals seem to do so only on behalf of an idealistic alternative, which inevitably falls short of their dreams.