Understandably, the Obama campaign made a strategic decision months ago to portray Romney as an extreme conservative, who was doubling down on Bush's failed policies, rather than as someone without principles who would say whatever was necessary to get elected.
This strategy was reasonable because: (1) Romney had appeared to tie himself irrevocably to the right-wing of his party during the debate; and (2) the allusions to prior, moderate versions of Mitt might have actually reassured some swing voters that he was really a pragmatist, despite the rhetoric of his campaign.
Now that we have seen Mitt in full Etch-a-Sketch mode, I believe that the Obama campaign has recognized a need to refine their attacks. But contrary to suggestions in some reports, I don't think that it is difficult to demonstrate that Romney is both unprincipled and extreme. In fact, I think Romney's recent maneuvering has made it easier.
Here is my modest, 4-step proposal:
(1) Continue to assert that during the primary season Romney went all-in, fully accepting every right-wing proposal and position;
(2) Demonstrate that he is now backtracking from the core of many of those positions, AND that he did so when the polls showed that he was losing;
(3) Thus, argue that we cannot trust what Romney says publicly, YET
(4) Maintain that, despite his recent about-face, Romney is beholden to the right-wing, AND will be CONTROLLED by the right-wing of his party.
The first 3-points are self-evident, but even the last point - the most critical - I believe, is also simple to establish. All the campaign needs to do is argue that the 47% video shows what Romney thinks and says in private, and from there it is a short step to the conclusion that he is beholden to the right wing. For good measure, challenge Romney to identify specific ways that he CURRENTLY disagrees with his own party.
One last observation: you'll note that I'm ignoring Mitt's record as a governor. That record could be used to solidify Mitt's image as a flip-flopper, but such references are wholly unnecessary, and could raise the danger that some voters might conclude he is a closer moderate.
I think this is a very simple approach and one that the Obama campaign will embrace with success.