Today, the Iran nuclear deal turns two years old. In its critics’ eyes, it has already failed.  President Donald Trump and many of his supporters complain that it has not changed Iran’s regional behavior, pointing to Tehran’s continued support for regional proxies and ongoing ballistic missile tests as proof. Other critics, including Senators Tom Cotton, Ted Cruz, David Perdue, and Marco Rubio, who wrote a letter to the administration denouncing the deal just this week, suggest that Iran may actually be violating it. They allege a range of technical violations, even though the International Atomic Energy Agency—and Trump’s State Department, for that matter—have confirmed Iran’s compliance.

In fact, the deal is doing exactly what is was supposed to do: prevent Iran from acquiring enough fissile material for a nuclear weapon, demonstrate to the Iranian public the benefits of cooperation with the international community, and buy time for potential changes in Iranian politics and foreign policy.

Anyone who thought a deal would immediately change Iran’s regional agenda or who maintains that, if only America and its partners had insisted on such changes in the talks they would have materialized, has a misguided sense of what sanctions and diplomatic pressure can accomplish. Having been deeply involved in the negotiations, we think it’s important to be clear about the purpose, enduring benefits, and inevitable limitations of the agreement.

The chief benefit of the agreement was to block Iran’s pathways to the bomb by freezing or reducing its capacity to produce the amounts of fissile materials required to do so—the most difficult step in the bomb-making process. Thus, as we know from the additional IAEA inspectors and 24/7 on-site cameras deployed as part of the agreement, Iran today operates only some 5,000 older-model centrifuges, maintains a much-reduced stockpile of enriched uranium, limits its centrifuge research and development programs, and has filled the core of its heavy-water nuclear reactor with concrete. Whereas experts assessed that, at the time of the deal, Iran was only months from being able to produce enough nuclear material for a bomb, under these new terms it is now at least a year away—plenty of time for the international community to anticipate any oncoming danger and respond accordingly.

Where would Iran be today without the agreement? It’s hard to know for sure, but even if Tehran had continued only to steadily expand its nuclear program as it had for the previous two decades, it would today likely be operating the more than 20,000 centrifuges it had at the time of the agreement. Iran would have continued enriching uranium and building its stockpiles, and it would’ve been operating a fully functional heavy-water nuclear reactor capable of producing enough plutonium for one or two nuclear weapons per year, all without the additional verification provisions put in place to ensure this was all it was doing.

What that means: Without the deal, Iran would today likely be only weeks from possessing enough weapons-usable material for a bomb. And without the verification procedures Iran committed to in the agreement, the international community would have no reliable way of knowing if it was stockpiling that material—until it was too late.

Critics assert that tougher sanctions and the threat of military force could have prevented Iran from arriving at this point. This argument does not hold up to scrutiny. Economic sanctions, even when progressively tightened over the years, never halted Iran’s program. When George W. Bush took office in 2001, Iran possessed only a few hundred centrifuges and no stockpile of enriched uranium. In the years that followed, Bush expanded U.S. sanctions and obtained three UN Security Council resolutions that all imposed real pressure on Iran. Yet when he left office in 2009, Iran had nearly 6,000 centrifuges, over 2,000 pounds of low enriched uranium (LEU), a partly built heavy-water reactor, and a secret underground enrichment facility.

Even after international sanctions were dramatically expanded and toughened in 2010 through 2012 under Obama, Iran continued expanding the quantity of its centrifuges, grew its enriched-uranium stock to more than 30,000 pounds, and build its heavy-water reactor—right up until the November 2013 Joint Plan of Action froze that program, paving the way for negotiations. It is wishful thinking to imagine that Iran, after expanding its program for decades despite heavy sanctions, would have miraculously decided in 2016 or 2017 to suddenly unilaterally refrain from any further nuclear advances, or even abandon its program altogether.

Critics also claim that the threat of force could have deterred Iran from expanding its program—another case of wishful thinking. Under Bush, who had a demonstrated willingness to use force in the Middle East, the United States refrained from any military strikes against Iran, even as it developed its nuclear program and killed U.S. soldiers in Iraq. As Obama’s critics accurately point out, it is not enough to threaten to use force: you actually have to follow through if your red lines are crossed.

If the nuclear deal went away, would the Trump administration, or any administration for that matter, bomb Iran if it expanded its uranium stockpile once again to, say, 1,000 pounds? What about 2,000? And what about ballistic missile tests? It is legitimate to argue the risk of an Iranian bomb is so high that the United States should use force to prevent it, and accept the consequences. But it is not persuasive to simply assert that Iran would have walked away from its entire nuclear program in the face of a more credible threat.

None of this means that the Iran negotiations were perfect. Of course it’s possible that the Obama administration and its partners could have gotten more in certain areas from Iran; just as easily, holding out could have scuttled a deal. What seems unlikely, though, is that Iran would have accepted any of the critics’ proposed “improvements.” The deal that many of them say they wanted—where Iran not only abandoned its entire nuclear program, but also agreed to stop interfering in the Middle East—was never in the cards.

It is true that Iran’s behavior in the region has not improved. It continues to prop up the murderous Assad regime in Syria and to fuel sectarianism by supporting proxies in Yemen, Lebanon, Iraq, and Bahrain. But it is also true that this behavior, which has gone on for years, including when Iran was under the toughest sanctions, cannot be attributed to the nuclear deal. Making Iran’s regional interference part of the agreement would have been a recipe for failure, resulting in both an increased nuclear threat and persistent Iranian meddling in the region. The reality is that, for Iran, supporting its regional proxies is relatively cheap, and absent a broader policy change (which should remain a U.S. goal), is likely to continue regardless of the regime’s economic health, which remains mediocre.

While a boost in revenues from unfrozen assets and increased oil sales obviously provides some scope for additional spending on military activities or terrorism, the regime also has a strong interest in allocating the bulk of any new revenues to its growing population, whose potential discontent is ultimately a greater threat to the regime than any Sunni neighbor. While the regime will seek to distribute some financial gains from the nuclear deal to its security forces, the “preponderance of the money [from sanctions relief] has gone to economic development and infrastructure,” according to General Vincent Stewart, director of the Defense Intelligence Agency.

The idea that a windfall from sanctions relief has turned Iran into an economic powerhouse fails to take into account the degree to which collapsing oil prices have undercut some of the financial benefits Iran has received. While the lifting of sanctions has allowed Iran to increase its oil exports by some 730,000 barrels per day since the agreement was reached, the price of oil since the negotiations began fell by around $40 per barrel—some 50 percent compared with average prices over the decade preceding the deal. As a result, Iran is earning less from its annual oil sales now than it did every year of the entire period from 2001 to 2011, even if it is selling around the same amount of oil.

While access to once-frozen revenue provides Iran with additional resources to spend on destabilizing activities—witness the recent, modest increase in the Iranian Revolutionary Guards Corps’s budget—the overall revenue stream is not nearly what it was prior to 2011. And given the new realities of the global oil market it is unlikely to return to the previous levels. Iran’s foreign policy is a big problem, but not primarily because of new resources from the Iran deal.

The debate over how the nuclear agreement is faring will shape the Trump administration’s Iran policy. As a candidate, Trump called it the “worst agreement ever negotiated” and promised to “dismantle” it. Upon taking office, however, he seemed to realize there we no good alternatives, and that a unilateral breach would pave the way for Iran to resume its nuclear program and turn America into the pariah that facilitated that outcome. In April 2017, Secretary of State Rex Tillerson grudgingly certified that Iran was complying with the deal while denouncing its behavior and announcing a comprehensive Iran policy review.

Options for altering the nuclear deal, however, remain limited. Unilateral abrogation now is no more appealing that it was in January. Meaningful renegotiation—of an agreement negotiated by six international powers and endorsed by the entire Security Council—is a fantasy. More likely, then, will be pledges to confront Iran and enforce further sanctions (such as those in a new bill targeting Iran’s ballistic missile program, conventional weapons acquisition, and the IRGC). The nuclear deal permits such sanctions, which remain an important tool of U.S. policy. But the risk will be the temptation to impose “backdoor” nuclear sanctions that Iran and others would consider a violation of the agreement. Supporters of the deal should be wary of sanctions designed to try to destroy it.    

There are also reports that some within the Trump administration and outside groups are advocating for an explicit policy of regime change, despite America’s dubious track record in the region. That Iran and the region could use a new government in Tehran is not in doubt. Significant anecdotal evidence and repeated electoral results suggest that the Iranian regime is unpopular and the country’s youth are desperate for change. But it is far from clear that an explicit U.S. policy to bring about that change—let alone overt or covert U.S. support for Iranian minority groups—(suggested recently by Senator Cotton) will bring a transition to a more democratic, peaceful, and pro-Western regime.

What the deal has done, at least for the next decade, is remove any realistic threat of a near-term Iranian nuclear weapon. The United States should use that decade wisely: standing up to and imposing costs on Iranian transgressions, supporting U.S. allies in the region, making clear to the Iranian public that the West is not an enemy, and preparing for the day when some of the deal’s restrictions will no longer apply. If, by 2030, Iran has not demonstrated that its nuclear program is exclusively peaceful and that it is willing to live in peace with its neighbors, the United States and its international partners will have difficult decisions to make about how to handle the issue going forward.

But since there is a chance that Iran will have different leaders or policies by then—the current Supreme Leader will almost certainly be gone, and a new generation may have come to power—why make those difficult decisions now? The Iran deal has bought valuable time. Squandering that time without a better plan would be foolish.