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Agreed to in July 2015 by the U.S., Iran, and five other nations, the 159-page long deal – officially titled the Joint Comprehensive Plan of Action -- came after twenty months of tense negotiations.

If you don't feel too keen on reading the agreement cover-to-cover, here’s the basic gist:

What’s the main goal?

The number one goal (from the U.S. perspective) is to prevent Iran from developing a nuclear weapon. Iran has agreed to restrict many of its nuclear programs, and allow international inspectors access to sensitive sites. In return, the U.S., the European Union and the United Nations will lift economic sanctions that have helped cripple Iran’s economy over the past ten years.

Who’s involved besides the U.S. and Iran?

Representatives from five additional countries were involved in the negotiations: the United Kingdom, Russia, China, France and Germany. The non-Iranian side of negotiations is often referred to as the P5+1 (permanent United Nations Security Council members + Germany) or the EU3+3 (three EU members + the U.S., Russia, and China).

How would it stop Iran from making a nuclear bomb?

The deal is designed to increase Iran’s “breakout time.” That is, the time it would need, given its resources, to produce enough weapons-grade uranium to build a nuclear weapon. Right now, Iran’s breakout time is estimated at roughly three months. The Obama administration argues that the deal would increase Iran’s breakout time to at least a year.

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Specifically, the deal would cut off Iran’s access to two materials used to manufacture nuclear weapons: highly enriched uranium and plutonium. Both of these are so-called fissile materials, meaning they can sustain the kind of chain reaction that powers a nuclear weapon.

Both are derived from raw uranium, which is a fissile material that can either be spun around in a centrifuge (creating enriched uranium) or irradiated in a nuclear reactor (creating plutonium). The deal aims to limit Iran’s ability to complete these two processes.

Here how:
- Restrictions on uranium enrichment: Under the deal Iran can continue to enrich some uranium for peaceful purposes. But it restricts enrichment to one facility (for the next 10 years), and limits the enrichment level to under 4 percent (for 15 years). Uranium at that level of enrichment is useful for operating nuclear power plants, but not enough to be used to produce a weapon. Iran has also agreed to eliminate most of its stockpile of enriched uranium, and to scrap two-thirds of its centrifuges.

- Restrictions on plutonium: Iran’s heavy-water reactor in in the northern city of Arak, which today could potentially produce enough plutonium for a nuclear weapon, will be redesigned and converted to a research facility. The reactor’s spent fuel -- also a weapons risk -- will be moved out of the country. Iran has also committed to not building another heavy water reactor for fifteen years.

The International Atomic Energy Agency (IAEA) is tasked with verifying that Iran actually does these things, and the deal spells out in some detail how these inspections will work. In return, economic sanctions against Iran will be lifted.

What are the sanctions all about?

The U.S. first placed sanctions against Iran in 1979, under President Carter, when Iranian revolutionaries seized the U.S. embassy in Tehran and overthrew the U.S.-backed government. In 1987, under President Reagan, the U.S. raised the stakes by blocking the import of all Iranian goods. These early sanctions were intended to “compel Iran to cease supporting acts of terrorism” and to generally limit its power, according to the Congressional Research Service.

More recent sanctions have focused more specifically on curbing Iran’s nuclear program. In 2005, the IAEA found evidence that Iran had flouted certain nonproliferation rules. The UN and the EU joined the U.S. in imposing additional sanctions, which restricted other countries’ trade and financial dealings with Iran. Sanctions have made it difficult for Iran to sell oil, one of it’s biggest and most lucrative exports, and limited the technology and materials the Iran can acquire. As a result, the value of Iran’s currency – the rial –has dropped precipitously over the last decade, while the cost of everyday goods continues to rapidly rise.

The nuclear deal promises to lift many of these sanctions. Sometime in the first half of 2016, the IAEA will verify that Iran has implemented its end of the deal. Once the IAEA gives the thumbs-up, most UN, EU, and U.S. nuclear-related sanctions will be lifted. However, other sanctions related to terrorism and human rights violations are set to remain in place.

What happens if Iran cheats?

If any of the signatories to the deal have reason to believe that Iran is cheating, they can appeal to an eight-member commission – representatives of the seven parties, plus the EU -- tasked with enforcement. This group then has 35 days to try to resolve the issue; if they cannot, the matter gets passed on to the UN Security Council. Sanctions will then automatically “snap back” into place, unless the Security Council votes unanimously to keep lifting them. (Setting this “snap back” as the default basically ensures that UN sanctions on Iran can’t be lifted without U.S. approval.)

How will we know if Iran is cheating?

That’s the question a lot of Republican skeptics are asking. Under the deal, the IAEA does not have so-called “anytime, anywhere” access to Iran’s facilities. In certain cases, inspectors might have to wait up to 24 days for access to certain sites -- a compromise that some experts find troubling. But overall, most nuclear security experts that have weighed in on the issue seem to agree that the monitoring and verification provisions are about as good a deal as could have been negotiated under the circumstances. In July, a bipartisan group of sixty national security experts released a statement arguing that the deal’s monitoring provisions would be “highly effective.”

How have key players reacted to the deal?

In the U.S., Republican leaders have been overwhelmingly critical. Speaker of the House John Boehner called the deal “unacceptable, and it’s been universally panned by GOP presidential candidates. In one notably hyperbolic instance, Mike Huckabee warned that the deal “will take the Israelis and march them to the door of the oven.”

Hillary Clinton supports the deal, as do most congressional Democrats. However, a number of influential Democrat have recently announced their opposition, including Sen. Chuck Schumer of New York, who wrote that the Iran will “use the agreement to pursue its nefarious goals.” It’s widely suspected that many of these elected leaders have been influenced in part by powerful conservative pro-Israeli lobbying groups like the American Israel Public Affairs Committee, which strongly opposes the agreement.

In Iran, President Hassan Rouhani praised the deal on Twitter, and polling suggests that most Iranian citizens support the deal. Supreme Leader Ayatollah Ali Khamenei has been circumspect, praising negotiators while heading off any idea of U.S.-Iran reconciliation. Some hardliners like former president Mahmoud Ahmadinejad are against the deal, arguing that it undermines Iran’s security.

In Israel, Prime Minister Benjamin Netanyahu slammed the deal as “a historic mistake.” Other conservative Israeli leaders have also been overtly critical: Education Minister Naftali Bennet called it “one of the darkest days in world history.”

In Saudi Arabia, Iran’s other major regional enemy, the deal has received a lukewarm reception. Although the Saudis express support for a nuclear deal, leaders there have cautioned that if Iran tries to “incite turmoil in the region,” it should expect “harsh and determined responses.”

In Russia, President Vladimir Putin said in a statement that his country welcomed the agreement and that the world had “breathed a sigh of relief” at the deal’s completion. A similar view is held by the European nations that participated in negotiations.

What happens next?

The UN and the EU have already approved the deal. Congress has until September 17 to review it. Congressional Republicans plan to issue what’s called a “bill of disapproval,” that rejects the deal. The Democratic leadership is currently trying to round up enough votes to filibuster that bill, and it's unclear if they’ll be able to. But even if they don’t, and the bill of disapproval is passed, President Obama is guaranteed to veto it. And as we found out Wednesday, the Senate won’t have enough votes to override that veto. So, barring any extraordinary circumstances, this deal is -- well -- a done deal.

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That said, fierce opposition will continue to rage into the foreseeable future. GOP presidential candidates Ted Cruz and Donald Trump have already planned a joint rally against the deal, and we can expect both Republicans and Democrats to lean heavily on the Iran as a key issue in the 2016 election. The political fight has also deepened divisions within the America's Jewish community, bringing a new level of vitriol to an old debate over how best to support and protect Israel.

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The Iran Nuclear Deal Explained