A deal is possible, but the ball is now very much in Iran’s court.

The latest round of talks in Geneva raised hopes of a negotiated outcome to the decade-long Iranian nuclear crisis. Pressured by sanctions, a new and more open Iranian leadership seems ready to compromise, and the P5+1 countries (the five permanent members of the UN Security Council plus Germany) have all expressed a strong preference for a negotiated outcome that would accommodate some of Tehran’s demands.

The P5+1 have shown their readiness to lift sanctions, offered some flexibility on low-level enrichment in return for precise demands on increased transparency and international monitoring, and set clear expectations on the most sensitive issues (including the Arak heavy-water reactor and the stockpile of 20 percent–enriched uranium). These are all necessary steps to reestablish trust and in no way impede Iranian “inalienable rights” to the peaceful use of nuclear energy.

It is now up to the Iranian leadership to make a strategic decision to engage in a process that will constrain and contain the country’s military nuclear ambitions in return for the progressive lifting of sanctions. President Hassan Rouhani and Foreign Minister Mohammad Javad Zarif have publicly expressed a willingness to provide the necessary reassurances. Iran should now demonstrate its good faith by accepting a far-reaching deal and game-changing commitment backed by the country’s supreme leader.

The answer is a qualified “yes.”

Any final agreement with Iran, if it comes to pass, will include necessary control measures to make up for the mutual mistrust that still characterizes relations between Iran and the international community. There will be no deal without clear qualitative and quantitative limits to Iran’s nuclear program as well as strict measures to ensure transparency. Interim steps toward such a deal, such as halting the 20 percent enrichment and freezing some sanctions, will be revocable.

Even an end-state agreement between Iran and the P5+1 will not directly translate into trust. Mutual suspicions weigh heavily: Iran still suspects the West of seeking regime change or a weakening of Iran’s regional position; Western and regional powers believe that Iran could still try to produce a nuclear bomb.

Will Iran cheat? That is possible, of course, but with a deal in place, any attempt to “break out” by transgressing limitations and safeguards would be detected early enough. Most likely, however, Iran will honor an agreement once it is concluded and will seek to use the rapprochement with the United States to enhance its regional geopolitical influence. In the long run, that serves Iran’s national interest better than a bomb.

We can believe in a deal with Iran, provided the West learns the lessons from a decade of failed negotiations: stay united and keep up the pressure, or Tehran will cross the nuclear weapons capability threshold.

President Hassan Rouhani’s rhetoric may be less obscene than that of his predecessor, Mahmoud Ahmadinejad, but that does not mean the regime’s nature and strategic outlook have changed.

Far from being a moderate, Rouhani has been a central figure in the Islamic Republic since day one. He shares direct responsibility both for the regime’s human rights crimes and for nuclear deception. He has repeatedly boasted how, as Iran’s lead nuclear negotiator in 2003–2005, he used the talks to advance the country’s nuclear program.

Since Rouhani’s election, Tehran’s domestic suppression and its support for international terrorism and the massacres committed by Syrian President Bashar al-Assad have continued as relentlessly as Iran’s nuclear program. And that program, as the International Atomic Energy Agency has documented, includes not only enrichment but also nuclear triggers, warheads, and delivery systems.

According to IAEA data, Tehran has now enough low-enriched uranium to fuel six nuclear warheads after further enrichment. Iran could produce one bomb’s worth of weapons-grade material in just seven weeks—faster if it used its second-generation centrifuges.

To roll back Iran’s nuclear program, the West needs to continue with tough sanctions coupled with a credible military threat.

We can believe in a deal with Iran. Significant progress has been made at the talks in Geneva, and it is evident that Iran has real interest in reaching an agreement that would halt sanctions. Allowing “managed” International Atomic Energy Agency access to the Gachin uranium mine and Arak heavy-water reactor is the first progress in five years.

However, in terms of national security, belief must be built on a solid foundation of independently verified evidence, permanent effective verification, sufficiently high default costs, and backup plans.

As in any political deal, each side must also earn the other’s trust. Iran’s IAEA track record signals a need for caution and enforced compliance. A long-term deal will therefore require full “unmanaged” IAEA cooperation, halting uranium enrichment beyond 3.5 percent, abandoning plutonium production, and ensuring effective permanent control mechanisms. An agreement should also establish a clear regulation that automatically reestablishes current sanctions in case of default.

Ultimately, a deal will depend on both sides accepting the best possible agreement and on convincing hard-liners that preventing Iran from obtaining a nuclear weapon would increase security and stability in the Middle East. An effective settlement would also achieve benefits far beyond the region, as the international community would prove its ability to prevent countries from acquiring nuclear weapons.

Those who oppose a deal with Iran need to accept that the lack of an agreement has led to the current situation.