On Megan McArdle's claim that "we cannot pay for social security by ending the Bush tax cuts on high earners": McArdle writes: "The [CBPP claims] we could, by simply refusing to extend the Bush tax cuts on high earners, cover virtually all of the Social Security shortfall.... But this is not the case.... [O]ur debt is not yielding 5.25% right now... [but] around 3%..." She says no, but the reality is yes, we could. Interest rates are low during recessions and high during booms. Odds are that as the economy recovers interest rates will rise and average about 5.25% in the future--which is what the CBPP needs for its calculation to be correct.