Speaking on behalf of the Bush administration, Vice President Dick Cheney vows that the U.S. will not allow Iran to have a nuclear weapon. He also will not take the military option off of the table (click here to see the story).
In this case, I think the administration is doing the right thing. Sometimes saber-rattling achieves more than "speaking softly while carrying a big stick."
Do you remember the "Axis of Evil"? It's Iraq, Iran, and North Korea. If Iran thinks that Bush is not serious, they have another thing coming.