I know that sounds hyperbolic, but it's vitally, vitally important that the president understand that if he goes after Social Security, the Republicans will turn the argument on him just as they did with "death panels" and "pulling the plug on Grandma" and end up solidifying the senior vote for the foreseeable future and further alienate the Party from the liberal base. I know it makes no sense that Republicans would be able to cast themselves as the protectors of the elderly, but in case you haven't been paying attention lately, politics doesn't operate in a linear, rational fashion at the moment. After all, the Republicans just won an election almost entirely on the basis of saving Medicare.
I think the least-commented on but important bit of information about this election was that the only semi-real policy issue that was on the table (lots of ad time) was Medicare, with Republicans telling everybody that Obama had cut Medicare. It was truthy not true, but they ran on it nonetheless. Any politician that votes to cut these things is telling voters, "please vote me out office," and, yes the Republicans will have no troubles styling themselves as the defenders of Social Security.