For over two years negotiations have been taking place between the P5+1(U.S., China, Russia, U.K., France, and Germany) and Iran over its nuclear program, which Iran claims to be for peaceful purposes but is widely believed to have the goal of developing a nuclear weapon. In June of 2013, Hassan Rouhani, considered a moderate relative to Iran, was elected President. He signaled wanting a less hostile relationship with the rest of world. A few months afterward October of 2013, negotiations ramped up. In November of that year, an interim agreement was reached in which Iran would halt its nuclear program. The U.S. agreed not to put on any new sanctions.
However, negotiations were less than successful. The U.S. wanted to halt Iran's nuclear program, limit to several hundred centrifuges, be able to re-instate sanctions if Iran broke the deal, a gradual removal of sanctions, to ship fuel out of Iran, and limit breakout time to over a year. Iran wanted immediate sanction relief, to be able to keep many of its 18,000+ centrifuges, a shorter breakout time and to be able to keep most of its nuclear program.
Because of the huge gaps, talks were extended from July 2014 to November 2014. Some gaps were closed, but not enough to make a deal, or even a framework, so they were extended March 31, 2015. Negotiations hit a pitfall once Iran signaled its unwillingness to ship nuclear fuel out of the country, backing out of hypothetically shipping its fuel to Russia in exchange for commercial fuel rods. The talks kept going until the last minute, and then were extended to a day later, and then again to April 2nd.
Finally, last minute, a framework was reached. The outline for this deal includes cutting centrifuges by two-thirds to about 6,014 with 5,000 allowed to enrich uranium, extending breakout time from 2-3 months to over a year. Several of Iran's reactors, notably in Arak and Fordow, will be redesigned but not closed. Fordow is burried under a mountain, was hidden until 2009, and will be able to keep 1,000 centrifuges, but won't be able to enrich uranium. Two-thirds of its centrifuges and infrastructure will be removed. The sanctions will be lifted in phases but can be reinstated if Iran breaks the terms of the treaty. It will be subject to stringent IAEA inspections. Iran has agreed to ship spent nuclear fuel, but not its nuclear stockpile. Research and development can continue, but not any allowing it to get within a 1 year breakout time. However, after 10 years, Iran can rebuild its nuclear program. In fact, Obama admitted that it could build a bomb after 13 years under the framework.
Despite the framework, things began to unravel quickly. About a week after the framework was agreed to, the Iranian supreme leader stated that sanctions must be lifted immediately once a deal finalized. The U.S. insists that the sanctions be lifted in phases. While this may get sorted out, it is not promising that a key disagreement came up so soon after the framework was agreed upon.
The final deadline if June 30, 2015, but it may be extended once again.
With Iran so close to bomb, there are only 3 options: a deal, allow Iran to get a nuke, or a regional war. The first one is optimal. If this latest dispute isn't worked out in the U.S.'s favor, any deal would be a bad one. If a bad deal is reached in which the sanctions were lifted immediately, they could cheat and the sanctions would have to be put on once again. This is a possibility with any deal. If a deal is reached, it could be rejected the Senate, but under the deal Obama made with Congress, it would take 67 votes to override any deal the President makes. Still, I think that nearly any deal would be preferable to no deal. The only exception would be if the sanctions were to be lifted immediately, and the inspectors wouldn't get access to the facilities. In this case, it would be very difficult to monitor Iran's activities and the sanctions would have to be re-instated.
Allowing Iran to get a nuke is highly undesirable for several reasons. It would deeply damage Israeli and Saudi trust in U.S. since it has repeatedly said Iran will not develop a nuke. It could also cause an nuclear arms race in the middle east. A four way nuclear standoff between Iran, Israel, and then probably Saudi Arabia and Turkey would be awkward enough. If Iran or Saudi Arabia, both known to sponsor terrorism, were to give a nuke to a third party organization, or more likely a terrorist group were to obtain a nuke if these authoritarian governments fell, the situation could go down hill very quickly. Lastly, it would make a mockery of the U.S's policy of nuclear-nonproliferation.
A war is undesirable. While it would allow the U.S. to prevent Iran from getting a nuke, and the weakening of Iran would likely topple Assad and the Houthi rebels in Yemen, and force Iran to engage less in militaristic activity, it would also be incredibly expensive. It could also costs thousands of lives. Russia is arming Iran, and may arm Iran even more with a war. In fact, the war could easily expand into a regional wide sectarian war. If the U.S. opts with bombing Iran because of a bad deal, it would likely destroy consensus with isolating Iran, especially with Russia and China. Unilateral strikes would also likely hurt the U.S. popularity in the muslim world. Iran could close the Straight of Hormuz, where a large amount of the world's oil comes across.
Strikes wouldn't even be very successful. Best case scenario is about four years being set back, after which Iran may be even more dedicated to getting a weapon. This would incur most of the costs of a full scale war with few of the benifits. The U.S, would really need a full scale continuous war. Securing the Straight of Hormuz would need to occur simultaneously with strikes on Iran's nuclear facilities. Ground operations may be necessary to destroy the centrifuges. This would probably lead to a full scale war with Iran and its proxies. In this scenario, there would certainly be American and Israeli casualties. Despite this, if it comes down to it I would reluctantly choose war, but only if the U.S. is willing to engage in a prolonged effort to prevent Iran from getting a nuke, partition Iraq and Syria and prevent the region from completely falling apart. This could cost trillions of dollars. This would have to come from somewhere else such Social Security or Medicare.
In the past Prime Minister Netanyahu's warnings about Iran developing a nuclear weapon were exaggerated and sometimes flat out wrong. Despite this if the deal fails, the remaining options will show he was right to bring it to the world's attention very early on. Had serious negotiations started in 1992 when Iran was decades from a nuke, rather than so recently, the U.S. would not be facing such difficult options.