The following citation is taken from an article describing the "Special Relationship" between the US and Britain:
"Concerning Iraq, the President and Prime Minister discussed the pro’s and con’s at length – and more intimately than among any other two world leaders. There was ample opportunity for the UK to influence US thinking – and it did so. The fact is that then-Prime Minister Blair made his own decision: It was too risky to allow Iraq to develop weapons of mass destruction (which even France and Germany believed they had), and then possibly pass them to terrorists.
This was not only the Prime Minister’s view, it was confirmed through a vote of Parliament. The special relationship did not make Britain do anything. Rather, it gave Britain unique information and access, and Britain – Government and Parliament alike – chose to go forward. And as former Prime Minister Blair candidly and courageously told the Iraq Inquiry, he would do it again."
Well, with Iran we are there again. The difference is that the US military is exhaused according to an article on DN.se. I'm not sure I agree but it would be interesting to know if it is economically too risky to enter into a fight with Iran about their bomb making. In this case we have a situation that would not be acceptable that we cannot do anything about. Does this financial debacle that we have entered put us in a situation of great risk for WMD proliferation? Is this the major problem today?