If a defense system stops only one missile from hitting one city, it will have paid for itself a dozen times over, but I don't want to hash that out here.

To be fair, I'm not sure what Obama's position on this issue actually is, so I might be pleasantly surprised.

On the Obama White House website, we have this:

National Missile Defense: The Obama-Biden Administration will support missile defense, but ensure that it is developed in a way that is pragmatic and cost-effective; and, most importantly, does not divert resources from other national security priorities until we are positive the technology will protect the American public.

Still not sure what this means, but at least it's an open issue.

We have a pretty good idea of Bush's views on missile defense.

This is from Bill Clinton.