The window of opportunity for Iran is beginning to close. Once nuclear weapons are in their hands they could be hidden away and, the clock starts on when they will use them. One nuke would be all it takes to wipe out Israel. A nuke in any major city of a country would cause a complete economic collapse. Once Iran has these nuclear weapons, there would be too easy to hide and no way to take them out. You would have to strike Iran before they could use them.
The worse part of this is that such weapons could be quietly smuggled into their targets in pieces and reassembled. When they were set off, you may not be able to prove which country they were from. Thus, you would have no basis to retaliate against Iran. Iran could keep pumping out these nukes without anyone able to do anything. This is exactly what we feared that Saddam would do in Iraq.
The point made in Keegan's last 'graph, which I quoted in comment $1.
When they were set off, you may not be able to prove which country they were from.
We need a new Bush Doctrine. Any nuclear attack on the USA will be met with massive US retaliation on every nuclear-armed states that we consider to be a possible perp.
(Another reason never to place lawyers in the White House.)