• President Donald Trump withdrew the US from the Joint Comprehensive Plan of Action (JCPOA), also known as the Iran nuclear deal, in May 2018.
  • The Iran deal was one of the crowning diplomatic achievement's of former President Barack Obama's tenure, but has continued to be a divisive issue in Washington since it came to fruition in 2015.
  • Withdrawing the US from the deal was one of the biggest and most controversial foreign policy decisions Trump has made yet.
  • Since Trump withdrew the US from the JCPOA, tensions between the US and Iran have steadily risen and reached a boiling point in recent months
  • Iran has taken several major steps away from the nuclear deal since July, exacerbating tensions with the US and Europe.
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President Donald Trump in May 2018 announced the US government is withdrawing from the Iran nuclear agreement, which marked one of the biggest foreign policy decisions he's made since entering the White House.

Trump's decision was highly controversial, especially given three of America's top allies - France, Germany and the UK - were strongly opposed to this move.

The president has long described the deal as "terrible," and while the pact has many proponents, he is hardly alone in this view.

The Iran deal - formally known as the Joint Comprehensive Plan of Action (JCPOA) - was one of the crowning diplomatic achievements of former President Barack Obama's tenure, but it has continued to be a divisive issue in Washington since it came to fruition in 2015.

Read more: The oil tanker attacks could make a US-Iran military showdown inevitable, experts warn

Since Trump withdrew from the Iran nuclear deal, tensions between Washington and Tehran have steadily risen and reached a boiling point over the summer - roughly a year after the president announced the US was pulling out.

Oil tanker attacks in the Gulf of Oman and an attack on two major oil facilities in Saudi Arabia have not helped matters, as both sides continue to issue threats, raising concerns that another war in the Middle East could be on the horizon.

The situation became even more tense in the early days of 2020 after the US announced it killed Qasem Soleimani, the head of the Iranian Revolutionary Guard Corps-Quds Force, in an airstrike. Iran's top diplomat called the incident an act of "international terrorism."

Meanwhile, Iran has taken several major steps away from the JCPOA, exacerbating tensions.

To understand the polarizing nature of this deal, why Trump's decision continues to face criticism, and the geopolitical implications of both the US and Iran stepping away from it, here's a quick breakdown of the historic pact and the debate surrounding it.

The Iran deal, explained

In July 2015, Iran and six countries reached a historic agreement called the Joint Comprehensive Plan of Action (JCPOA), popularly known as the Iran nuclear deal.

The six major powers involved in these negotiations with Iran were known as the P5+1, which stands for the United Nations security council's five permanent members (the US, France, the UK, China, and Russia) and Germany.

The deal came together after two years of intense discussions and aimed to restrict Iran's ability to develop nuclear weapons in exchange for lifting economic sanctions against Tehran.

Read more: Iran could be risking war over the Saudi oil fields because it deliberately wants to spike up the price of oil

As part of the deal, Iran agreed to reduce its number of centrifuges - tube-shaped machines that help enrich uranium - by two-thirds. It also agreed to reduce its stockpile of enriched uranium by 98% and limit uranium enrichment to 3.67%.

In other words, Tehran agreed to restrictions that would allow it to have enough enriched uranium to maintain the country's energy needs, without having the ability to build a nuclear bomb.

On top of this, Iran agreed to give access to inspectors from the International Atomic Energy Agency (IAEA), the UN's nuclear watchdog agency, to its nuclear facilities, among other facilities. The IAEA has repeatedly found Iran to be complying with the terms of the pact.

In January 2016, when the IAEA declared Iran was living up to its end of the bargain, all nuclear-related international sanctions against Iran were lifted.

The controversy surrounding the Iran deal, explained

Iran and the US have been enemies for decades. The two countries have an extremely complex history that involved a CIA-orchestrated coup in the 1950s, a pro-American puppet monarch who was overthrown in 1979 via the Islamic revolution, and the infamous hostage crisis at the US embassy in Tehran that followed the uprising.

The constant threats from Iranian leaders against Israel, America's top ally in the Middle East, and chants of "death to America" in Iranian streets have also not helped matters.

In this context, there is a massive distrust for Iran in the US (and vice versa), and Washington has long feared what might happen if the Iranian regime developed a nuclear weapon. Iran made great strides in this regard by the 2010s, hence the Obama administration's efforts to orchestrate the nuclear deal. When the pact was finally settled in 2015, it was widely celebrated as a major diplomatic achievement.

But many (primarily conservative) leaders in Washington still felt the Iran nuclear deal didn't go far enough to limit the country's ability to develop nuclear weapons.

This is because the Iran deal contains sunset clauses, or parts of the agreement that will ultimately expire. Under the deal, the restrictions on Iran's centrifuges go away after 10 years (in 2025) and the limitations on uranium enrichment disappear five years after that (2030). Hence, there are fears that once these restrictions expire, Iran could rapidly develop a nuclear weapon.

"It is clear to me that we cannot prevent an Iranian nuclear bomb under the decaying and rotten structure of the current agreement," Trump said in May 2018. "The Iran deal is defective at its core. If we do nothing we know exactly what will happen."

More broadly, Trump, among others, has argued the deal didn't do enough to address Iran's regional behavior or its missile program. Accordingly, the president wants to negotiate a new deal with Tehran.

Iran has begun to step away from the deal amid fears of a war with the US

Trump's unilateral decision to withdraw the US from the JCPOA in May 2018 was promptly condemned by US allies, who have scrambled to find a diplomatic solution ever since.

For roughly a year after Trump's controversial announcement, Iran remained in compliance with the JCPOA. But the Iranian government in early June announced it would break from a key component of the JCPOA by ramping up its enrichment of low-grade uranium and increasing its stockpile beyond the limitations outlined in the deal.

Making good on this threat, Iran in July announced it had surpassed the deal's cap on how much low-grade uranium it could stockpile - 300 kg or about 660 pounds. It also announced it had breached the deal's limitation on uranium enrichment - 3.67% - but has only enriched up to 4.5% and far below weapons-grade levels.

Read more: Sen. Chris Murphy says Trump is blindly risking conflict with Iran and could spark a war even if he doesn't want one

In September, Iran took yet another big step away from the deal when it announced it would begin developing more advanced centrifuges that allow for more rapid uranium enrichment. Iran also said it was lifting all limits on research and development. Wendy Sherman, who served as the Obama administration's lead negotiator on the JCPOA, described this move to Insider as of "serious concern."

"It's all concerning, because it's moving away from a framework that ensured Iran would not get a nuclear weapon," Sherman said. "Iran is not just being emboldened but is being left in some ways to take actions that say they will not be pushed back. We are at a very, very difficult place."

Iran in early November announced it was taking a fourth step away from the 2015 nuclear deal - injecting uranium gas into 1,044 centrifuges that had been kept empty under the terms of the agreement.

Since Trump withdrew the US from the JCPOA, his administration has pummeled Iran with crippling economic sanctions. Simultaneously, Iran has accused the US of waging "economic war" and has rejected proposals from Trump to hold talks unless the US lifts sanctions and returns to the JCPOA, perpetuating an impasse that is making the wider world increasingly nervous.

Critics of Trump say that his decision to withdraw from the JCPOA has unnecessarily sparked a global crisis and increased the prospect of war.

"There is a direct line you can draw from Trump's violation of the Iran deal and the risk of conflict today," Jon Wolfsthal, who served as the nuclear expert for the National Security Council under Obama and is now a senior adviser at Global Zero, recently told Insider.

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