For the past few weeks, the Obama campaign has had their sights pointed squarely on Mitt Romney. In a shift, they just started throwing Rick Santorum into the mix (and under the bus) in their criticisms of GOP economic policy.
Do they really believe some of the national polls that show that Santorum has a chance at dethroning the Republican Establishment's choice for candidate?
There may be more possibilities, but I see three reasons for the change:
1) They have analyzed the scenarios and think that Santorum has a real chance, particularly if he can win one or both primaries on February 28th. It would give him momentum going into Super Tuesday 8 days later if he can pull from Romney's native state of Michigan and an upset in Arizona could boost be enough for people to start writing Romney, Gingrich, and Paul off.
2) They still think Romney will win but they want to prolong the race as long as possible to keep the attacks up. By giving "respect" to Santorum in the form of campaigning against him, they would be fueling the fire of his base.
3) Like the rest of us, they don't really know who will win in this roller coaster primary season, so they're just hedging their bets.
The other very unlikely scenario is that they feel they're positioned better against Romney for the general election and are hoping to quell the Santorum possibility without taking him completely off the map.