The swarm of journalists killing time in the lobby of Geneva’s Intercontinental Hotel can finally go home. A deal has been reached between Iran and the P5+1 (Germany and the five permanent members of the UN Security Council, including the United States) in the ongoing dispute over the Iranian nuclear program. It’s not a final deal--all sides say they want something more comprehensive--and it’s only set to last six months. Yet it’s a remarkable step forward. The Iranian nuclear issue had smoldered for a decade. The diplomatic process appeared useless, if not dead. Only three things changed: Iran enriched more uranium, the world imposed more sanctions, and the risk of war grew. The new deal stands in the way of all three, but its value is broader. American and Iranian diplomats were meeting openly, and were apparently able to hammer out their differences on an important issue. A little more trust between the two states could yield benefits elsewhere. And the deal itself isn’t so bad, at least according to details released by the White House.

Iran agrees to stop enriching uranium to 20 percent, and to “dilute or convert its entire stockpile” of 20 percent enriched uranium within six months. This is reassuring. Taking a unit of raw uranium and producing 20 percent-enriched uranium from it requires far more effort than getting that 20 percent up to the 90 percent or so needed for a typical nuclear device. A large stockpile of 20 percent enriched uranium would let Iran create warheads (if it chose to do so) relatively quickly. Diluting or converting Iran’s stockpile makes that take longer, giving monitors and intelligence agencies more time to find them out and giving international leaders more time to craft an appropriate response. Iran had previously resisted restrictions on its 20 percent enrichment--a worrying indicator, given the few peaceful uses such uranium has. A step back from 20 percent enrichment sends a more positive signal about Iran’s intentions.

More importantly, Iran agreed to significant restrictions on the centrifuges it uses to enrich uranium. The faster-working centrifuges that Iran has been developing won’t be used, and Iran won’t be installing new centrifuges. Iran has a lot of centrifuges that have been installed but aren’t yet operating, and the deal appears to keep those from starting up (the White House’s statement isn’t entirely clear, but it is clear that the number of centrifuges enriching will stay roughly the same). And Iran agreed to not build new enrichment facilities, a reversal from what they had suggested was their plan. More enrichment facilities would have compounded the diplomatic disputes, and they’d have made monitoring more difficult.

The heavy-water reactor under construction at Arak, which could allow Iran to make a plutonium-based nuclear bomb, also faces significant restrictions. Meaningful construction will stop. This is a victory for the West--the previous round of talks had broken down after France took a tough stance on Arak, insisting that the interim deal include halting construction. Something like the French position appears to have prevailed, and while it might not have been absolutely necessary to get to this point as quickly as Paris wanted (there are other milestones later in the reactor’s deployment that could also have served as stopping points), it’s better than what we might have expected, even in a final deal.

Crucially, Iran made major concessions on international monitoring of its nuclear facilities. Observers now get daily access to the enrichment facilities at Natanz and Fordow, potentially giving swifter notice if Iran does decide to bolt for the bomb. They also get more access to Arak, including details of its design that had been kept under wraps. And Iran will make some disclosures that would be required if it signed on to the stringent Additional Protocol of the Nuclear Non-Proliferation Treaty, a good omen since getting Iran to sign the Additional Protocol is a key goal of a final deal. But most importantly of all, the facilities Iran uses to make centrifuges will now be monitored, making the diversion of centrifuges to any hidden enrichment facilities harder. This will also allow verification of another element of the deal. Iran agreed not to build up a big stockpile of centrifuges while the deal is in effect, which would have allowed the nuclear risk to continue growing even as negotiators work.

What did we have to give up to get all this from Tehran? The U.S. will suspend key sanctions on Iran’s (already faltering) auto industry and on its trade in gold and oil; Iran will also get access to some of its money being held overseas. And some of the most controversial sanctions, such as restrictions on repairs to Iranian airliners, will also be lightened, while measures will be taken to increase Iran’s access to humanitarian goods like food and medicine. Lifting these restrictions could be win-win, since Iran and its apologists will have a harder time convincing the world that, a la 1990s Iraq, the sanctions are creating enormous human costs. Other governments will face less pressure to push back on the more effective parts of the U.S. sanctions regime.

The deal isn’t perfect. The West made major concessions on its old goals--once upon a time, the aim was “stop, ship and shut,” that is, that Iran would stop enriching uranium, ship its stockpile of 20 percent uranium abroad, and shut down the deeply buried enrichment halls at Fordow. In this deal, Fordow will still be running, Iran’s stockpile of 20 percent uranium will stay in-country, and enrichment will continue. But Iran’s nuclear program and politics had long ago created facts on the ground that made “stop, ship and shut” unrealistic. It’s a loss for the West--had those goals been realized, the risks to international security from the Iranian nuclear program would have been smaller.

There are also some gaps. Long-running concerns about a military facility at Parchin that may have hosted explosives tests needed for developing a nuclear warhead have been put off to the final deal. And it’s not clear whether Iran will still be able to design and test advanced centrifuges, provided it doesn’t use them to enrich. If it successfully does and the deal breaks down, it might begin manufacturing a new generation of more advanced centrifuges several times more productive than the rather primitive IR-1s in use now.

The deal also puts a lot of pressure on international monitors and intelligence agencies to ensure compliance. They’ll need to assure the world that there aren’t hidden enrichment facilities or centrifuge factories. Iran is unlikely to let inspectors traipse around the entire country looking for these things, so the world may have to rely on satellite pictures, spies, and other imperfect tools to monitor Iran’s compliance. There are already rumors of hidden sites--an affiliate of the terrorist group Mujahedin-e-Khalq (the MEK) announced one just last Monday. These can be hard to verify, and even unverified can be exploited by figures eager to wave the bloody shirt against Iran. It’s hard not to see a parallel to the period before the invasion of Iraq, where hard-to-solve factual questions became severely politicized, ultimately allowing a march to war.

And there’s another challenge with the rollout of the deal. President Obama, in an apparent sop to those who want more sanctions now, stated that if Iran reneges, America will “turn off the relief and ratchet up the pressure.” The official White House fact sheet on the deal expresses similar willingness to raise sanctions if things fall apart. While the sanctions regime did a lot to get Iran to this point, it’s not clear how much more it can be expanded in an internationally sustainable way. Things will be even hazier if last night’s deal breaks down in a way that doesn’t turn all the key countries against Iran. Obama’s move to appease his critics may merely box him in, forcing him to take a step in a future crisis that could either escalate it or inadvertently gut the sanctions regime. And either way, some of Obama’s critics don’t appear satisfied. The Senate can bring a House bill strengthening sanctions to the floor if it chooses, and Buzzfeed reporter Rosie Gray tweeted within hours of the deal’s announcement that a senior Senate aide told her “the sanctions...will be voted into law when Senate returns from recess.” The administration has threatened a veto--a weapon President Obama has been hesitant to wield, and which will be especially difficult to use now, with Obama at the weakest he’s been in his entire presidency. If worst comes to worst--say, if his veto gets overriden or the sanctions waivers he’ll have to issue to implement the deal face serious legal challenges--the White House text does leave some wiggle room: the Western countries agree to “Not impose new nuclear-related sanctions for six months, if Iran abides by its commitments under this deal, to the extent permissible within their political systems.” (Emphasis mine.)

Finally, what happens when something inevitably goes wrong with the negotiations process? While yesterday’s agreement gives plenty of cause for optimism, there are too many players, too many variables, and tremendous pressure for everything to go as planned. If a final deal can’t be reached, the indefinite perpetuation of the present arrangement wouldn’t be terrible, as it does put obstacles in an Iranian path to the bomb. Living with this deal forever would be easier for us than for Iran, which still faces painful sanctions like exclusion from the international financial system. Iran certainly has incentives to come to the table with a serious offer in the next six months. But Iran’s leaders might face sabotage from hardliners, or might see Supreme Leader Ali Khamenei again push for a tougher line. The comprehensive talks could also break down in a way that makes key countries blame America more than Iran, endangering the integrity of the sanctions regime and potentially letting Iran off the hook. And this isn’t implausible. Even if Iran tries to hold up its end of the bargain, bad or biased intelligence like I discussed above could make key Congressmen think Iran’s breaking its promises. And then, as a congressional aide told Buzzfeed, “Congress will move forward because Congress believes that, at the very least, after six months, if Iran doesn’t do what we need them to do, Congress will drop the hammer...When six months comes up, the administration will have no leeway with Congress.” Some on our end might be too ready to toss a deal that isn’t so bad.