Here’s something I don’t understand about the politics of the issue. Maybe readers could help me out here.

A lot of liberals don’t want to cut Social Security benefits even for the affluent. They think the program enjoys strong political support because it is not seen as a welfare program–because it is structured in a way to create the illusion that people take out what they paid in, or at least to create the sense that what people take out is reasonably related to what they paid in. So means-testing benefits would cause the program to unravel politically. Some liberals think, for the same reason, that it’s important to keep paying for Social Security benefits out of payroll taxes, and not out of general revenues. Having a dedicated tax makes it seem less like another welfare program.

I can understand this line of thinking, even if I disagree with it.

But liberals are generally fine with the idea of raising payroll taxes on high earners. Barack Obama signaled his openness to that idea again last night. He advanced this idea as a way to make the program solvent. Presumably he does not intend to increase high-earners’ future benefits to adjust for the higher contributions he would extract from them. (If he did, his fix would cover only 24 percent of the program’s shortfall.)

But if a benefit cut would make rich people stop supporting Social Security, why wouldn’t a tax increase have the same effect? Is the theory that rich people can’t do math?