If the Trump administration is serious about taking on Iran in the Middle East it must transform its strategy in Syria for fighting the terrorist Islamic State of Iraq and al Sham (ISIS). Our current strategy will only continue to strengthen Tehran’s grip on the region.

The US needs a new approach that gives it the independence and leverage it needs to begin pushing back successfully.

It won’t be easy. The strategy the administration inherited from President Obama sees Iran as a partner in the fight. The U.S. has therefore done nothing to contain the dramatic and alarming Iranian expansion of military power in Syria.

Yet the expansion was avoidable.

Tehran had used Syria as a base for Lebanese Hezbollah, HAMAS, and its own subversive activities for decades at no cost. The 2011 uprising against Syrian President Bashar al Assad was a blow to its position. Therefore Iran rushed to support Assad, sending in special Qods Force operatives, then advisors from the Islamic Revolutionary Guards Corps (IRGC).

As the revolt against Assad deepened, Tehran added thousands of fighters from Lebanese Hezbollah and Iraq’s Shi’a militias. Conventional combat forces of the IRGC joined in when a Russian air campaign in support of Assad started in late 2015.

Today, Iran commands tens of thousands more fighters in Syria than it did before the Arab Spring uprising. It has established its own military headquarters and embedded troops and advisors so deeply in the Assad regime that it cannot survive without them.

President Obama not only saw Iran as an ally against ISIS, but also feared that weakening Assad would hand Syria over to ISIS and al Qaeda. Washington’s single-minded focus on ISIS enabled the expansion of Iran’s military footprint and will continue to do so.

The U.S. fear was unfounded in 2011 and 2012, when secular forces dominated the opposition to Assad. Obama’s failure to support the opposition at that time was an enormous missed opportunity.

But now, Al Qaeda has thoroughly co-opted the opposition. Current American strategy, with its anti-ISIS focus, has thus trapped us in a dilemma. Defeating ISIS in the current situation will leave Iran permanently entrenched in Syria and the U.S. will have no partner on the ground it can use to weaken Iran’s position.

This dilemma requires a counter-intuitive solution, which we have outlined in a report, America’s Way Ahead in Syria.

The U.S. must reframe its strategy away from the rush to retake territory from ISIS and toward building a new Sunni Arab partner force that can fight Al Qaeda as well as ISIS—and that we can ultimately support against the Iranian presence in Syria and the Assad regime.

We will not find such a force in northern Syria, where our current military efforts are concentrated.

The neighboring Turkish government has helped its proxies, heavily infiltrated and partly controlled by Al Qaeda, to dominate the opposition in the north, especially after the fall of Aleppo destroyed the last remaining acceptable opposition forces there.

The U.S. currently relies on minority Kurdish forces in Syria. They cannot form the nucleus of a Sunni Arab opposition movement even though they have brought some Sunni into their campaign.

The problem is not primarily ethnic—Arab vs. Kurd—but rather political. The Kurdish objective of carving out an autonomous or independent Kurdish zone, thereby precipitating the partitioning of Syria, alienates the overwhelming majority of Syria’s Arabs. We will not be able to build an Arab partner in Syria on the basis of that political program.

The U.S. must therefore shift the focus of its efforts to southeastern Syria, where neither the Kurds nor Al Qaeda have yet coopted Sunni tribes. We must send troops to fight alongside the tribes, first against ISIS, then ultimately against Al Qaeda, Assad, and the Iranians.

Only then will we escape the dilemma that paralyzes us—the fear that weakening Iran and Assad will hand Al Qaeda or ISIS the victory.

We’ve tried the hands-off, no-boots-on-the-ground approach for six years, and it has brought us to this unacceptable dilemma.

This is no call for a 2003-style invasion of Syria. The U.S. must work primarily through local partners. But we must choose the right partners, not the most expedient ones.

In the current situation, when no good partners exist, we must help create them.

Kimberly Kagan is the president of the Institute for the Study of War, a Washington, D.C,-based think tank