Some numbers from the proposed Budget for 2009 for the Federal government. I try to divide non-security spending crudely into necessary spending (courts, justice, Treasury, the mysterious "other" mandatory spending) and "worthy causes" (things that are really discretionary).
Update: Figures in parentheses are from FY 2000, when we ran a $200 billion surplus. I am estimating as best I can from these tables
(*Domestic worthy causes = Agriculture, Commerce, Education, Energy, Health and Human Services, Housing and Urban Development, Interior, Labor, Transportation, NSF)
Personal income taxes: $1259 billion ($1004.5)
Corporate income taxes: $339 billion ($207.3)
Social Insurance receipts: $949 billion ($652.9)
Other taxes: $153 billion ($161)
Deficit: $400 billion (surplus $236 billion)
Message to Republicans: if you cut spending on "worthy causes" to zero, you still would not balance the budget. You will have to raise personal income taxes.
Message to Democrats: if you increased personal income tax receipts by 25 percent (a ginormous tax increase), you still would not balance the budget. You will have to cut back on "worthy causes."
Message to the AARP: if Social Security and Medicare continue to be "untouchable," then y'all had better buy guns, because in twenty years there won't be any money left to pay for national defense, much less for any "worthy causes."
Update: Today's Lead Editorial in the Washington Post is about Obama, Clinton, and McCain ignoring fiscal reality. One note that I would make is that tax increases (cuts) tend to add (subtract) less revenue than is typically projected, because of the way people adapt to them. I also suspect that spending programs often cost more than is projected, because projections seem to err in that direction.
Also, in response to a comment, I added estimates for these categories for FY 2000. That was a fantastic year for personal tax receipts (also for "other" taxes), thanks to the Internet Bubble. But note how much lower Medicare and Social Security were relative to Social Insurance receipts. The unfunded prescription drug benefit is probably the big reason for the adverse move since 2000, although the rise in health care spending and the gradual increase in the ratio of beneficiaries to workers will be the main factors going forward.