But there's a catch.
The emerging deal doesn't touch on any of the nasty stuff Iran does around the Middle East — not even a little bit. Helping Syria's President Bashar al-Assad slaughter innocent Syrians, funding Hamas in Gaza and Hezbollah in Lebanon, supporting dangerously sectarian militia groups in Iraq: not a peep about any of that in the newly inked agreement at Lausanne.
In one sense, that was a necessary evil. Getting Iran to voluntarily restrict its own nuclear program is hard enough without asking the country to restructure its entire foreign policy. But the deal, in some ways, will make the problem of Iran's harmful regional foreign policy harder to solve: Iran will be more free to act as it pleases in the Middle East, and have more money with which to do that, if the deal is fully implemented.
Even the best things can have dark sides.
This deal gives Iran a lot more money to play with
There is one reason, and one reason only, for Iran to agree to the serious limits on its nuclear program imposed by the Lausanne deal: relief from crippling international sanctions. And that's what it gets if it complies with the deal, though from the information we have now, it's not exactly clear when that would happen.
Some sanctions — like the American ones punishing Iran for its ballistic missile program and support for terrorism — will remain in place. But post-deal, Iran will be in a much stronger economic position than it was beforehand, taking in potentially billions of dollars per month that it wouldn't otherwise get access to.
And for the deal to work, the sanctions have to stay dropped. The only incentive Iran has to comply with the deal is the threat that sanctions will be re-imposed if it cheats. If new sanctions were imposed over, say, Iran's involvement in the Syrian civil war, Iran would have fewer reasons to stick to its pledge not to develop a bomb. Any Western nation that tries to put new economic pressure on Tehran puts the deal at risk.
Sanctions aren't the only, or even necessarily the best, way for the United States to deal with Iran's nuclear behavior. But the nuclear program ties America's hands in other ways. The intense diplomatic focus on striking and maintaining a deal will make a major diplomatic push on Iran's other issues harder — the State Department's resources and staff aren't infinite. There's also a chance the United States won't want to aggressively confront Iran in other places — like Iraq, where it's supporting powerful and hyper-sectarian Shia militias — for fear of jeopardizing the nuclear deal.
Bottom line: Iran will have a lot more money in tax revenue and oil sales to play with, and the US and its allies will be in a weaker position to make sure that money isn't spent on violence.
It's pretty unlikely that this deal will make Iran more moderate
You might think this logic could cut both ways. Iran, fearing new Western sanctions and a return to international isolation, might curb its support for Syrian President Bashar al-Assad, Hamas, and Hezbollah. The nuclear deal, on this theory, is the first step toward bringing Iran into the international community.
But this misunderstands the real reasons behind Iran's bad behavior in the Middle East. What most of the world sees (correctly) as unacceptable support for tyrants and terrorists, Iran's leaders see as necessary for its security. There's every reason to believe Iran will keep doing terrible things to the Middle East after a deal — and will do it with more money and international legitimacy.
Iran is currently locked in what political scientists call a "security dilemma" with its Sunni neighbors — especially its great regional rival Saudi Arabia. In a security dilemmas, neither side can really trust the other's intentions to be peaceful toward the other: Saudi Arabia and Iran have a decades-long history of enmity and ideological tension. So one side, fearing attack, ramps up defense spending or supports a regional proxy in order to guard against a perceived threat. The other side sees that as threatening — what if they're planning to attack? — and feels compelled to respond in kind.
This creates a self-sustaining cycle in which both countries take actions that are designed to make their country more secure, but end up scaring the other side and thus raising both the chances and the potential severity of conflict. "It's what the US and the Soviet Union were involved in" during the Cold War, Daniel Serwer, a professor at the Johns Hopkins School of Advanced International Studies, explains.
A nuclear deal won't make Iran's fears about Saudi intentions go away. That means Iran will continue to do whatever it can to ensure that it, its allies, and its proxies are stronger than the forces on Saudi Arabia's side — much like the US and the Soviet Union in the Cold War.
Iran will continue to intervene in Syria's conflict, because it believes Assad's collapse would remove one of its most important allies in the region. It will continue to support hardline Shia militias in Iraq, as they serve as leverage to ensure the Iraqi government never becomes hostile. Hezbollah fills a similar role in Lebanon. Ditto Hamas in the Palestinian territories — with the bonus of hurting Israel, which the Iranian leadership also hates for ideological reasons.
If anything, we should expect this activity to be stepped up after a deal. With more cash and fewer levers of international pressure, Iran will be in a stronger position than ever relative to its enemies in the region. Ayatollah Khamenei may be a bad person, but he's not stupid — he can figure out how to press an advantage when he's got one.
That doesn't mean the deal is bad overall
Here's the really devilish thing about the strengthening-Iran problem: it'd be true of any nuclear deal, no matter the terms.
Think about it: the basic problem is that once the international community agrees to relax sanctions in exchange for nuclear concessions, its leverage over Iran gets weaker and Iran gets richer. The specific terms of the nuclear deal — enrichment, inspections, centrifuges, whatever — are irrelevant.
That means there are basically two options. The first is a nuclear deal that empowers Iran. The second is no deal, and instead keeping sanctions up. The problem with that approach, though, is there've been sanctions on Iran for quite some time, and during that period they've made a lot of progress on their nuclear program. Sanctions alone won't cause Iran to capitulate, which means that keeping sanctions up indefinitely is basically a recipe for Iran to keep developing its nuclear program.
In the simplest terms, that means you've got a choice between relaxing sanctions and the Iranians getting a bomb (or at least getting close enough that it'd be impossible to stop them from getting one if they want). And that's assuming that the sanctions regime would be maintained indefinitely without a deal, which is unlikely — international buy-in for sanctions is premised on the idea that they'll eventually produce some kind of a deal. If it looks like the United States doesn't ever want a deal, the Russians and the Chinese might eventually balk.
And it's worth reiterating that this deal is really, really good at limiting Iran's nuclear program. On the most important issue, inspections designed to ensure Iran doesn't cheat on the terms of the deal, the Iranians conceded astonishingly wide latitude to look at its nuclear facilities and supply chain.
"I would give it [the deal] an A," Aaron Stein, a nuclear proliferation expert with the Royal United Services Institute, told Max Fisher, "because of the inspections and transparency."
Yes, the deal will strengthen Iran. But the terrible truth is that there's probably no good alternative.
WATCH: 'President Obama announce nuclear deal with Iran'