Substantively, I’d want to see everything in the $4 trillion deal before making a global comment on how good or bad it is. But politically, a deal that raised less than half as much in taxes as the fiscal commission, lifted the Medicare eligibility age and cut Social Security benefits by more than $200 billion would lead to a liberal backlash that dwarfs anything we’ve seen so far. I think it might well spark a (futile) primary challenge.

Which is not to say it wouldn’t be good politics for the White House. Whenever you think about the Obama administration’s political incentives, you need to keep this graph in mind:

Democrats like compromise. Independents like compromise. Republicans don’t. That’s an asymmetry between the two parties that the White House would be very happy to exploit going into 2012.