The Republican strategy
Obstruct, obstruct, obstruct -- block whatever the Democrats are trying to do, or at least force them to compromise it as much as possible. Limit the Democrats' achievements as much as possible.
To what purpose? To fuel cynicism and pessimism -- the most destructive forces that can take root in any movement -- within our side. To get people moaning that the Democrats can't get anything done, that they are sellouts. To get people talking about staying home in November or voting third-candidate. That's the Republicans' goal. Because all of that, no matter what motivations underlie it or what message it is intended to send, will have the practical effect of empowering Republicans.
Would any of us really punish candidates who share 80%-90% of our philosophy and empower the very people whose relentless obstruction prevented getting much of what we wanted enacted? Relatively few, I think, but that's all the Republicans need. In a close race, just 5% of the base staying home or voting for a third candidate could be enough to tip a seat from blue to red. And after that, all that matters is that the seat is red instead of blue. It makes no difference how or why it happened.
For the record, I don't think it will work. Obama seems to have suffered very little loss of popularity with the liberal base from January to December, and elections are won or lost in the center, which (unless something major and unexpected happens) will vote mostly on the basis of whether unemployment has improved by November or not. But be alert for the effects of the Republican strategy, and be ready to recognize them when you see them.