The biggest thing to scare Bush about Iran is not nuclear weapons but is the same weapon that Saddam used against the US. All oil worldwide is sold in $USD and Saddam started selling it in €uro's back in November 2000 which meant that the US was losing out big time in both the selling of the stuff and in buying it for it's own needs. Iran is going one step further and is planning to start it's own oil exchange this year which will also be based on the €uro with lot's more backing than just them so if analysts are correct they may succeed in bankrupting the US and putting them along the same lines as Africa because of their record level of debt.

Here are some links about it. I can't verify the content but it does make for interesting reading.

[www.tacomapjh.org]
[en.wikipedia.org]
[www.energybulletin.net]