US and Iranian negotiators in ongoing nuclear talks must deal not only with their counterparts across the table, but also with the challenge of second-guessing another country’s internal political dynamics. This game reached absurd levels this week when, in an attempt to derail the talks, a group of Republican US Senators sent an “open letter” to Iran claiming that any deal could be undone by a future president. President Barack Obama mocked what he described as an “unusual coalition” between the US and Iranian hardliners. Indeed, the efforts undertaken by vocal hawks in both countries make a sensitive and fragile process even more so.

While Iranians observe this American rift, perhaps wondering who’s in charge, the US team likewise tries to decipher the landscape in Tehran. In Washington, a question I’m often asked is “who are we actually dealing with?”

The options that come to mind are Supreme Leader Ali Ayatollah Khamenei (whose influence on the negotiations I wrote about here), the moderate government of President Hassan Rouhani, and the Islamic Revolutionary Guard Corps, or IRGC.

The IRGC is perhaps the most perplexing of all these major stakeholders. In the West, its name is synonymous with anti-Americanism and undermining US influence and interests, either directly or through proxies in the Middle East. But what is the IRGC, really, and where does it stand on the ongoing negotiations?

Guardians of the revolution. After toppling the Shah of Iran in 1979, the country’s new regime established the IRGC as a paramilitary force. The Islamic Republic’s goal was to provide an alternative to the traditional military, which the revolutionaries saw as pro-monarchy and untrustworthy. The new government executed some of the top commanders and generals who had served under the shah, and others fled the country. The Iranian military, once one of the top five powerhouses in the world, essentially collapsed.

The subsequent Iran-Iraq War, which lasted from 1980 to 1988, was devastating for Iran but turned out to be an opportunity for the new regime led by Ayatollah Ruhollah Khomeini and the Revolutionary Guards he deployed to the front lines. During the revolution, Khomeini had led only one of many factions, but during the Iran-Iraq war he consolidated his power. The war also allowed the IRGC to establish itself as a new military, and it came out of the eight-year conflict empowered.

Since then, the IRGC has co-existed with the military but remains a separate entity. It undertakes some of Tehran’s most important operations. The Basij—a large internal security force under the authority of the IRGC—is often at the forefront of responses to domestic unrest, for example during the 2009 crackdown on protests against the disputed reelection of President Mahmoud Ahmadinejad. Outside the country, too, it is the IRGC that leads many of Iran’s most vital operations, including the current fight against the Islamic State in Iraq and Syria (ISIS). The elite Quds Force, also a branch of the IRGC, is particularly active throughout the Middle East. It is responsible for a number of covert operations and provides funding, training, and intelligence to Iranian proxies in the region, including Hamas and Hezbollah.

The IRGC is connected to Iranian nuclear affairs two ways: in its relationship to the regime of economic sanctions that are imposed on the country as punishment for nuclear activities, and in its direct involvement in the country’s nuclear and missile programs.

Travelers to Iran are often surprised to see the country’s infrastructure. Tehran doesn’t look like the capital of a state that has been under sanctions for more than three decades. Its three-level bridges, long underground tunnels, metro, and highways even put some US cities to shame, for which Iranians have the IRGC to thank. The paramilitary organization has turned obstacle into opportunity by becoming a major economic player, picking up business where the private sector hasn’t been able to deliver because of sanctions. The Guards have a number of firms, including the engineering company Khatam ol-Anbia, which the government hires as a contractor. The IRGC also fills gaps left by foreign companies no longer doing business in Iran, sometimes through smuggling: the Guards import goods that other companies can’t touch due to sanctions, as well as goods, like alcohol, that are banned by the regime.

The IRGC, thus, benefits from sanctions. To be clear, the number one entity the United States wants to weaken is actually one of the foremost beneficiaries of the current sanctions regime.

Nonetheless, the IRGC wouldn’t necessarily be damaged by a lifting of sanctions. As an organization it has proven to be highly adaptable over the years, and companies linked to the IRGC now operate beyond Iranian borders, drawing income from abroad. As such, the IRGC’s commercial activities will likely remain unaffected by the outcome of the talks.

Guardians of the bomb. There is evidence that the IRGC is involved in Iran’s nuclear program, even if the extent remains unclear. The Islamic Republic’s supreme leader, Ayatollah Ali Khamenei, is the commander of the armed forces and has direct supervision over the IRGC. Many analysts agree that the IRGC would likely have control over any nuclear arsenal, should Iran be able to produce one, but that the final say on whether to use the weapons would lie with the supreme leader.

Currently, the IRGC is the foremost player in Iran’s defense programs, including the country’s contentious missile program, which poses a security concern to regional and international players. (Tehran made it clear from the beginning of the nuclear negotiations that the missile program was off the table, and it’s safe to say that Foreign Minister Javad Zarif’s team doesn’t have a mandate to discuss it.) Beyond missiles, which could theoretically be used for either conventional or atomic weapons, the IRGC’s concrete involvement in the nuclear program has several layers. First, some of the country’s key contentious facilities were built on IRGC bases. This includes the Fordow enrichment site. Second, the IRGC is behind many operations involving dual-use materials, or those that have regular civilian uses but can also be used in missile and nuclear programs. Because the IRGC has a foothold in both civilian and defense projects, it uses a number of these items for both purposes. Third, a number of IRGC members are also scientists who have been involved in the nuclear program. These include Fereydoun Abbasi, the head of the Atomic Energy Organization of Iran under former President Ahmadinejad.

The IRGC and nuclear talks. In the United States, many are quick to equate Iranian hardliners with the IRGC, but the truth is more nuanced than that. Some of the most vocal critics of the negotiations are not linked to the paramilitary organization at all. The IRGC’s stance on the talks is, not surprisingly, very similar to that of its commander in chief, Khamenei, whose statements suggest that he is cautiously supportive. When Tehran and the world powers concluded their interim deal in November 2013, IRGC commanders expressed their support for the process and for Zarif’s team, while emphasizing the importance of respecting Khamenei’s guidelines.

Since then, IRGC commander Gen. Mohammad Ali Jafari has come out in support of (link in Persian) the negotiations again. Much like Khamenei, he has made comments that cautiously back the talks, while reminding the public that Washington isn’t trustworthy. In other words, the IRGC is somewhere between the Rouhani government and the hardliners trying to undermine its efforts to reach a deal.

The IRGC is often reduced to a caricature in the debates on Iran’s nuclear program. It is depicted as a monolithic group of fanatics driven by a desire to develop a nuclear weapon and use it. Its role in the program itself, to be sure, remains fairly obscure, but its stance on the ongoing negotiations is clearly relatively centrist. Because the IRGC, like Khamenei, has various constituents and interests to balance out, it is not as opposed to the prospect of a nuclear deal with the six powers as many believe it to be.