Unfortunately this looks like a serious possibility. I know that the entire rest of the world, with the exception of the Israeli leadership and the leaders of the Saudi royal family, want the Congress not to pass the current bills to impose further economic sanctions on Iran, just as the Obama administration has succeeded in getting an interim nuclear agreement on nuclear weapons with them, with negotiations ongoing to achieve a final agreement, which would almost surely be ended by the Congress passing these bills. While public opinion, including a solid majority of the US Jewish population, supports this agreement, we have a bipartisan group of Senators now approaching getting enough votes for this insane legislation to overcome a presidential veto. This is a new low for a body that has already put on so many shows of mass stupidity in the past, although this time there are a bunch of Democrats on board rather than it being some circus put on by Tea Party dingbats.
Iran's leader, Ali Khamenei, has issued fatwas against nuclear weapons. I have posted this point more times than I can count, but regularly when I tell people this, the reaction is, "Oh, he is just doing that to trick us." Not likely. He is a religious leader issuing a religious proclamation, and it should be taken seriously. Of course while Ahmadinejad was president it was easy to ignore that Khamenei was really in charge and to focus on all the crazy statements that Ahmadinejad would make on a regular basis.
Then there is the myth that if the US just presses hard enough, this will be like South Africa or the USSR and the system will collapse to be taken over by pro-US reformers who will abjure nuclear weapons. Well, first of all, US pressure on Iran, just like the sanctions on Cuba, simply allow hardliners in Iran to justify their repressions and general bad behaviors. However, the part that most people really do not understand is that the vast majority of Iranians, including openly and clearly the Green Movement opposition, support Iran having a civilian nuclear program, which is what the government has always claimed is what they are pursuing. If somehow a bunch of secular reformers were to overthrow the Islamic regime, they would continue the programs, although maybe then we would say it is OK. After all, the Iranian nuclear program originally started back when the Shah was in power with US assistance.
While passing the sanctions would end this round of negotiations and put the hardliners back in charge over reformist President Rouhani, the Iranians probably would not move to obtain nuclear weapons immediately because of Khamenei's fatwas. But he is old, and if it becomes clear that it is simply impossible to achieve any sort of agreement on the matter with the US, his successor as Vilayat-al-faqi might well overturn his anti-nuclear weapons fatwa, and war might well then be the result.
After all, two months after he became president, Bush ended the ongoing negotiations about nuclear weapons with North Korea, with advisers inspired by Nicholas Eberstadt's prophecies of the imminent collapse of the regime whispering in his ears. Instead, the North Koreans moved to obtain nuclear weapons, and their noxious regime remains in place, possibly worse than ever under the rule of Kim Jong-Un. A similar outcome in Iran would be highly likely if Congress passes this awful legislation.