Paul Ryan's Multiple Unicorns

Paul Krugman, writing about GOP Congressman Paul Ryan's proposed budget plan:

Notice the marked area at the bottom: Ryan is assuming that everything aside from health and SS can be squeezed from 12 percent of GDP now to 3 1/2 percent of GDP. That’s bigger than the assumed cut in health care spending relative to baseline; it accounts for all of the projected deficit reduction, since the alleged health savings are all used to finance tax cuts. And how is this supposed to be accomplished? Not explained. This isn’t a serious proposal; it’s a strange combination of cruelty and insanely wishful thinking.