Its hard to say without an in depth study of the cause for the major deficits, but certainly a lot of the debt can be traced to unpaid for continuous war. Iraq, when interest, and VA benefits are included has been estimated from 3 to 4 trillion. When Rumsfeld was Defense Secretary they found a trillion missing that no one could account for. Then I don't know about Vietnam, it was less, but with interest and verteran's benefits I suppose pushing a trillion. (It was before the inflation brought on by the Nixon Schock kicked in.) Then there was the unnecessary 30 years of cold war -- That's maybe a couple trillion.
I have no idea of how much of our corporate welfare is paid with borrowed money, but what you consider unnecessary and necessary would be highly debatable. For example the bulk of all our foreign aid comes back to our defense contractors as payment for weapon systems. So that's one form of corporate welfare. Is it necessary? I suppose if you work for Lockheed you'd say it is. Someone else might say it isn't, and so on.
Most people would say the New Deal Deficits were necessary, as were the TARP deficits, much of which has already been paid back. Cash for clunkers? You decide. It was corporate welfare, but it also saved jobs at a critical time. There might have been a better way to accomplish the same thing, but I'd rather see money spent there than for napalm, or another useless missile system.
Then you've got Commerce, HHS, DOE, DOEd, HUD, Labor, Homeland 'Security' , State, Interior, Treasury, DOJ, Transportation, and the VA. You decide what we don't need , and let me know. I've definitely got some ideas where cuts could come, and we'd all be better off.
Bottom line is you'd get a consensus maybe on a third to half the debt.
