Rand Corporation | Alireza Nader: US-Iran tensions are likely to rise in the coming months. The Joint Comprehensive Plan of Action (JCPOA) nuclear agreement between Iran and the P5+1 (United States, UK, France, Russia, China, and Germany) has been roundly criticized by President Donald Trump and others, including some lawmakers on Capitol Hill. The U.S. has declared Iran's recent ballistic missile tests to be in violation of UN Security Council resolutions, and top American officials have indicated a strong desire to contain and roll back Iranian influence in the Middle East.

The U.S. has many options at its disposal, including the use of military force. However, the current balance of power in the Middle East and Iran's position in relation to major regional and international powers is likely to limit U.S. options toward Iran. The JCPOA is widely regarded to be a success story, especially by the European Union, China, and Russia. But perhaps more importantly, the Islamic Republic is relatively stable at home and a power to be reckoned with in the Middle East. To be sure, the U.S. can apply much more diplomatic and economic pressure against Iran and even resort to military force, but Washington will face real limits in its ability to change Iran's behavior in the region or stop its growing missile program.

Iranian President Hassan Rouhani, seeking re-election in May, was able to achieve his major promise to Iranian voters; he delivered the JCPOA and released Iran from crippling international sanctions put in place during the presidency of Mahmoud Ahmadinejad (2005–2013). Many Iranians may rightly argue that Rouhani has not delivered much else; repression in Iran appears to have increased, and the economic benefits of JCPOA have not trickled down to the average person.

Yet Rouhani has achieved three important objectives: restoring regime stability, helping increase Iranian influence in the Middle East, and improving relations with major powers such as Russia, China, and much of the European Union. American critics of JCPOA often blame the agreement for emboldening Iran, but it should not be blamed as the chief cause of Iran's growing power. Domestic conditions in Iran and regional developments are the biggest factors.

Before Rouhani, Iran faced a major popular uprising over Ahmadinejad's contested 2009 election. Tehran and other major Iranian cities witnessed the largest protests since the Iranian revolution of 1979. Rouhani may not be immensely popular in Iran, but he is not as divisive as Ahmadinejad. He not only has the trust of the regime but also much of the public. Rouhani presents himself as a can-do official rather than an ideologue or inspirational leader. He has also bridged the gap between reformist groups and the conservative establishment, although the former is totally shut out from power and appears rather moribund. There are few indications of future unrest, although public dissatisfaction remains high. Iranian society is still divided, the regime is ever repressive, and the economy plagued by corruption and incompetence. But the Iranian regime is firmly in power, commands a vast security force, and has managed to heal divisions within itself for now. The death of Iran's Leader, Ayatollah Ali Khamenei, may create scenarios for instability, but the regime also appears to be preparing itself for a successful succession process. If there is instability, the Revolutionary Guards will surely consider the use of force to crush any insurrections, as they did in 2009.

If the U.S. attempts to foment strife in Iran by pursuing a policy of “regime change,” it is likely to face steep challenges that it may not be able to overcome. This will be especially so if the executive order banning Iranians from traveling to the United States is re-implemented. America has a relatively positive reputation among the Iranian public, but U.S. measures that hurt and humiliate the average Iranian will certainly decrease U.S. soft power regarding Iran.

Additional sanctions against Iran will hurt, but Washington should not jeopardize the JCPOA, even if it is by “a thousand cuts” (e.g. another temporary travel ban on refugees and citizens from Iran and six other Muslim-majority countries). Iran is unlikely to walk away from JCPOA, knowing that it would rather have the world blame the U.S. for the agreement's possible failure. A confrontational U.S. approach toward China, Russia, and the EU may even make those parties side with Iran in any future conflicts over the JCPOA.

In addition to finding more stability at home, the Iranian regime has achieved greater power in the Middle East. The so-called Islamic State should be given much credit for Iran's rise in the region. An avowedly anti-Shi'a group, the Islamic State has inadvertently allowed Iran to accumulate more power in Iraq and Syria and gain closer ties to major international powers such as Russia. Iranian allies such as Iraqi Shi'a militias, the Syrian regime, and Lebanese Hezbollah have been key in fighting the Islamic State and other Sunni Jihadi groups. Of course, the Syrian regime and Hezbollah have spent much of their energies fighting the Syrian opposition and not the Islamic State, but Iran has been able to paint itself as a force against violent Sunni jihadism.

Both the U.S. and Iran seek to defeat the Islamic State, even if their larger goals in the region may be opposed. This gives Iran extra leverage in the Middle East and with the United States. Iran commands a regional expeditionary force of thousands of Shi'a foreign fighters in Iraq and Syria. Hezbollah has also developed a larger and more experienced military wielding heavy artillery and tanks. They have gained greater battle experience in Syria and look likely to have achieved Iran's key goal of assuring the survival of the Assad regime. More importantly, Iran and Russia are now closely aligned in Syria and beyond. Iran, a junior partner susceptible to Russian manipulation, is nevertheless critical to the future of the Middle East. Its influence cannot be easily rolled back.

The U.S. and Iran differ on many issues, and tensions between the two once-allies may increase dangerously in the near future. But the U.S. would likely have more to gain by sticking with the complicated relationship that has defined ties between Washington and Tehran since 1979. Always foes, but not always fighting, the U.S. and Iran have begrudgingly tolerated each other. They even signed a major, and so far successful, non-proliferation agreement because it benefited both. America cannot change Iran, and Iran cannot defeat America in the Middle East. The U.S. and the Islamic Republic don't have to maintain formal diplomatic relations or be partners, but there are issues that affect both, including the Islamic State. America has many ways to pressure Iran, and sometimes it should use them. But killing the JCPOA by a “thousand cuts” or any other way will hurt American interests. Sometimes the U.S. has to make and stick with a deal. Even if it is with the bitterest of enemies.

Alireza Nader is a senior international policy analyst at the nonprofit, nonpartisan RAND Corporation.