It's all about momentum and sustaining a right left drift as opposed to the left right drift of the last 40 years.  However it's important also not to over-reach, as that could stall the whole process.  I think that's why Obama is trying to maintain a bipartisan consensus even though he doesn't have to on most issues, and even though he knows it will break down sooner or later.  The important thing is that he is seen not to have been the one to have reverted to the "business as usual" adversarial politics so hated by the "non-political centre"...

notes from no w here