Krugman points out there is a disconnect caused by how politicians have talked about federal spending for the last 40 years and the reality. Everyone is convinced there is an ocean of federal waste, funding armies of federal bureaucrats and welfare queens. Leaving aside the fact that spending on payroll is only 5% of the federal budget, "federal bureaucrats" turns out to include food safety inspectors, FBI counter-terrorism agents, and the unpopular auditors who actually collect taxes for revenue. So cutting them is something of a problem.
I do offer a slightly more charitable explanation for the confusion among the public. We have a lot of people who would like to see spending reapportioned, but there is not a lot of agreement on how. For example, I suspect that the majority of people who want to see education funding increased either have children or are expect to at some point. Not all, but the majority. A majority of folks who would like to see the money go to education may or may not also want to see the money go to infrastructure investment.
Still, you can't seem to get away from the fact that everyone believes there are lost of easily cut bad programs and waste, and somehow expect the "good" programs to miss the ax. For myself, I've gotten quite bitter about it to the point where I am rooting for the Tea Party folks to cut mercilessly. Perhaps some privation will remind people why we developed these programs in the first place -- and make them more willing to close corporate tax loopholes and raise taxes on those best able to bear the burden.