How should the U.S. go about cleaning up its debt mess? In a recent interview with MarketWatch, two of the world’s top economic minds — Professor Jeremy Siegel of Wharton and Professor Robert Shiller of Yale — offered their takes. Siegel says Medicare is the big issue the government needs to address, and he doesn’t think tax increases will be necessary. Shiller says a policy of “tax and spend” that gets more Americans back to work is needed, though he says it would be extremely unpopular. Neither Siegel nor Shiller thinks U.S. legislators will allow a debt default, despite the current struggle to reach a compromise on the debt ceiling issue in Congress.