I see Obama appearing to applaud.
Now, if you could come up with a screen shot of him appearing to actually join in the chorus of boos, that would be interesting.
OK, I watched the video, and I acknowledge the point.
Democrats stood up and cheered when Bush said "Congress did not act on my proposal to save Social Security". It turned into a chorus of boos.
The low resolution video doesn't really make it possible to pick out Obama. The screen capture could be from anything. But, with a little more work, this could be interesting.