Interest and military and take a distant third and fourth place respectively. Here are the rough proportions of the top US federal budget expenditures according to the Treasury Department:

- Healthcare (Medicare and Medicaid): 24%

- Social Security: 23%

- Net Interest on Federal Debt: 15%

- National Defense: 13%

And I'll point out that the enormous bill for the interest on debt is a pretty good reason to avoid ringing up so much debt in the first place.