Ramesh Ponnuru lists some of the ways that Obama has moved to the center since the midterm election. Obama isn't really moving to the center. He is moving into a consolidationist phase. Obama talked about how he admired Reagan because the Gipper "changed the trajectory of America in a way that Richard Nixon did not and in a way that Bill Clinton did not. He put us on a fundamentally different path because the country was ready for it." Well Obama has changed the trajectory of the US, and unless the trajectory changes, the center-left is in a good position to control the terms of debate.
The knowledge that he has already won the biggest fights and that he has put in place a set of political institutions and incentives that will tend to strengthen his side even after he has concluded a second term gives Obama a lot of room to move. It isn't that tough to sound and look moderate if you aren't actively trying to get Congress to pass bills that will shift the policy environment to the left. So you hire the Daley fellow as your White House Chief of Staff and you get some nice words from the Chamber of Commerce. You agree to extend the 35% top marginal income tax rate for a couple of years and you refuse to blame the opposing party for a madman's shooting rampage. You get some good headlines and you haven't given up anything important (and Obama has a much better sense of what is important in advancing left-of-center politics than many of his allies.) Obama is building fortifications around his biggest policy accomplishments.