What is going to be cut first? The defense budget, of course. The elderly vote disproportionately, so their benefits will remain difficult to tinker with, and large savings are not to be had there anyway - it is expensive to provide this care, and pushing the cost to the private sector won't make it cheaper. There is a limit to further cuts in the social safety net - at some point there will be riots in the streets. And again, even a very basic social safety net such as the US's is expensive: there's not much to be gained there.

But the US can cut its defense budget in half and still be the baddest kid on the block. Now, Obama could never contemplate such a thing - the GOP would rip him to pieces. But McCain has nothing to prove on the military front (in his mind), so he will reduce the defense budget drastically. Think Nixon and China.