Iraq war costs

Some startling numbers from Talking Points Memo on the Iraq war costs and social security:

Now, an interesting point of comparison is the projected shortfall in the Social Security budget, which is on the contrary tabulated on highly pessimistic assumption. That number over 75 years is projected at $4.7 trillion.

Now I hasten to add, again, that the Iraq numbers are highly optimistic and the Social Security ones highly pessimistic. If we do a simple back of the envelope calculation we get the 75 year cost of Iraq would be $3 trillion.