The deal is done: Iran has agreed to pause its nuclear program in exchange for some relief from international sanctions imposed by world powers, including the United States.

As it was advertised by the Obama administration, the deal is merely a "first step," designed to create six months of breathing room, during which Iran does not progress any closer to a nuclear weapon, and the U.S., Britain, France, Germany, Russia, China, and the European Union demonstrate their own willingness to deal by lifting some of the economic penalties they've levied on Iran to discourage its nuclear ambitions.

Over the next six months, Iran and world powers will negotiate toward a deal hat would guarantee Iran's nuclear program is peaceful, in exchange for a removal of all nuclear-related sanctions. That basic framework is spelled out in the preliminary agreement reached over the weekend.

But the deal could be tricky to implement, and a lot could go wrong along the way. Here's what has to happen and what could derail this progress.

WHAT IRAN HAS TO DO

1. Dilute half of its 20-percent enriched uranium. Iran is close to being able to build a nuclear bomb. Should it choose to race for a weapon, it would take Iran about one month to get there, according to the Institute for Science and International Security. It takes longer to make a bomb with diluted uranium, and downblending half of its 20-percent-enriched stock to no more than five percent, as this agreement requires, would bump Iran's nuclear "breakout time" to about two months, according to an ISIS estimate published last month.

2. Stop building its Arak reactor. Iran must stop construction on a heavy-water reactor at Arak, which would be capable of producing plutonium and give Iran an alternative path to a nuclear weapon.

3. No enrichment above 5 percent for 6 months. Iran must stop enrichment activities at two other plants and halt enrichment above 5 percent for six months.

4. Submit to increased monitoring. Iran must provide more information about its reactors to the International Atomic Energy Agency (IAEA) and allow inspectors daily access to its plants at Fordow and Natanz, plus access to uranium mines and factories that build reactor parts.

WHAT THE U.S. AND WORLD POWERS HAVE TO DO

1. No new oil sanctions. The U.S., U.K., France, Germany, Russia, China, and the European Union cannot impose new sanctions on Iranian oil exports.

2. Grant access to frozen Iranian funds. Iran has about $100 billion in funds in overseas banks, most of which it can't access due to sanctions, U.S. officials have said. Under this deal, Iran will be able to access some of that money.

The amount is already being disputed. Secretary of State John Kerry announced in Geneva that Iran would see $4.2 billion of that money, and another high-level U.S. official said Monday that it would be released over the course of six months. Iranian government spokesman Mohammad Baqer Nobakht, on the other hand, said Monday that the U.S. had already allowed the release of $8 billion in frozen Iranian money, Iranian state media reported. The White House has called that assertion "false."

Separately, world powers must also allow Iran to access some of its frozen oil revenues to buy humanitarian goods like agricultural products, medicine, and medical devices.

3. Lift other sanctions. The U.S. and its partners in this deal must lift sanctions on Iran's sales of petrochemical products, gold, and other precious metals. Kerry estimated these rollbacks to be worth $1.5 billion. Sanctions on Iran's auto industry will also be lifted, and Iran will be able to buy and install spare parts for nonmilitary airplanes.

WHAT COULD GO WRONG

Iran experts have called this agreement "modest" and noted that we'll find out more about the potential for a longer-term agreement as Iran and world powers begin negotiating under the framework laid out over the weekend in Geneva.

In the meantime, here's what could derail progress toward a broader deal:

1. Congress could pass new sanctions. The U.S. has agreed not to enact any new oil sanctions, and if Congress does so, it would invalidate the deal cut in Geneva. In order to do that, Congress would likely have to override President Obama's veto, and that's improbable at this point.

Senate Majority Leader Harry Reid, D-Nev., a usually staunch backer of the Obama administration, has voiced some appetite for new sanctions, and he intends to call a vote when the Senate returns from its Thanksgiving recess. Republicans have panned the deal and appear eager to undermine it with new sanctions, and Democrats like Sen. Chuck Schumer, D-N.Y., have criticized it, while others have praised Kerry and the administration for hammering it out.

"They will study this, they will hold hearings if necessary, and if we need work on this, if we need stronger sanctions I am sure we will do that," Reid said Monday in an interview with NPR.

"I just don't think Congress is going to shoot the country in the foot. Now what they will talk about is sanctions after" the six-month negotiating period," Gary Samore, executive director of the Belfer Center for Science and International Affairs at Harvard told reporters on a conference call Monday.

2. Iran could renege. They've done it before. "The last time there was a nuclear deal with Iran was in 2003, and that deal was with the British, the French, and the Germans, and Iran suspended many key parts" of its nuclear program, Samore pointed out. "The deal lasted two years and the Iranians reneged on it." Experts have said that Iran is much more likely to race for a bomb by building secret facilities than by advancing its enrichment at monitored reactors.

3. The sanctions regime could erode. Opponents of the deal have warned that, once the U.S. starts rolling back sanctions, nations and banks will be inclined to cheat, doing business with Iran in secret, in the hopes of evading the sanctions currently in place. Experts and U.S. officials have said this is unlikely.

"If you're a small bank on Malaysia that has very limited commerce with the U.S., if any at all … you might be more attracted to the Iranian market," said Ray Takeyh, an Iran expert with the Council on Foreign Relations. Any sanctions evasion is likely to come from "marginal" institutions in Asia, Takeyh told reporters on Monday.

4. Implementation could prove difficult. The text of the agreement is clear, but there's still room for interpretation. For instance, Iran must provide more information about its reactor facilities to the IAEA, but what if there's a dispute over the level of specificity, or access for IAEA inspectors?

There are "a number of implementation issues," Samore said. Implementation will be managed by a commission created by Iran and world powers to oversee it.

5. Other issues could further sour relations. It's hard to have a worse relationship than the U.S. has with Iran, but now that the two countries have taken a step forward, it's possible they could take another one back.

Among the unrelated issues that could further poison this newly working relationship, Syria tops the list. Iran is helping Bashar al-Assad remain in power in Syria by supporting his military, the U.S. has acknowledged, and now that the United Nations has announced a new round of talks on Syria to be held in Geneva in January, it's unclear whether Iran will attend. The U.S. has insisted that all participants agree that Syria must be led by a transitional government-almost certainly not including Assad.

Along with hopes that progress on the nuclear deal could mean cooperation on Syria's civil war comes the possibility that the dispute over Syria will intensify and pose a problem in the nuclear sphere.