If ISIS is going to be defeated, Muslims themselves must do it.

The mass shooting in San Bernardino last week should have confirmed what many Americans still refuse to accept: we can’t defeat ISIS.

That doesn’t mean we couldn’t destroy ISIS as an organization. A modest deployment of troops and materiel in Syria and Iraq would be sufficient. President Obama, in his determination to secure a legacy as the president who got us out of Iraq, refuses to do this. But it could be done.

That still wouldn’t solve the real problem, which isn’t ISIS’s territory but its ideology. ISIS would give way to another group, perhaps a resurgent al-Qaeda or maybe something worse. From the many-headed hydra of Islamic extremism would come a new threat, aimed at the West and at moderate Muslims in the Middle East and elsewhere, and we would once again be debating whether to deploy troops abroad.

The violent interpretation of Islam that animates groups like ISIS—and individual Muslims like Syed Farook and his wife Tashfeen Malik, the San Bernardino shooters—is not going away simply because we defeat ISIS on the battlefield, or proclaim, as Obama did Sunday night, that it “does not speak for Islam.” Our president is no more qualified to decide which Muslim groups espouse a correct interpretation of Islam than is our Secretary of State John Kerry, who on Sunday called members of ISIS “apostates.”

No. American political leaders, like pundits, are not in a position to weigh the doctrinal merits of ISIS. If ISIS is going to be defeated, Muslims themselves must do it—not just with bullets and bombs, but with a version of their faith that rejects political Islam and jihadist violence once and for all.

Many Muslims Aren’t Moderate

That won’t be easy, because the virtue of radical Islam, and ISIS, is disputed among Muslims across the world. True, the vast majority of the world’s 1.6 billion Muslims might reject Islamic supremacist ideology of the kind ISIS preaches, but there are tens of millions (perhaps far more) who embrace some version of it.

More than 70 percent of those polled, in a country with more than 175 million Muslims, were unwilling to express an unfavorable view of ISIS.

One recent poll from Pew illustrated the enormity of the challenge facing moderates. The poll asked Muslims in eleven countries with significant Muslim populations their opinion of ISIS. While majorities in every country except Pakistan had an unfavorable view of the group, a significant portion of respondents expressed favor (Turkey, 8 percent; Malaysia, 11 percent; Nigeria, 14 percent). Turkey, a country of nearly 75 million, is 98.6 percent Muslim, which means about 6 million Muslims in Turkey have a favorable view of ISIS.

In Pakistan, which is 96.4 percent Muslim, the results were even more shocking. Nine percent expressed a favorable view of ISIS, while 62 percent responded, “don’t know.” That means more than 70 percent of those polled, in a country with more than 175 million Muslims, were unwilling to express an unfavorable view of ISIS.

These poll numbers fit with a 2013 Pew poll of Muslim attitudes on a range of issues. In Egypt, 29 percent agreed that suicide bombing in defense of Islam is “often/sometimes justified.” That share represents more than 23 million people.

Islam Is Not a Monolithic Religion

Obama claims ISIS does not speak for Islam, but no one body or institution speaks for Islam. Muslims do not have the equivalent of a Catholic Pope or a Congregation for the Doctrine of the Faith to settle doctrinal disputes.

Malik and Farook were not ‘self-radicalized,’ they were radicalized by specific Islamic doctrines that are compelling to millions of Muslims worldwide.

But it’s hard to believe the president when you hear about men like Maulana Abdul Aziz, chief cleric of Islamabad’s Red Mosque. Last December, Aziz, who has no direct connection to the leadership of ISIS, made it clear that he and his followers respect ISIS and that “we support the organization which wants to implement the Islamic system.”

As it happens, authorities now believe Tashfeen Malik had some connection to Aziz’s mosque in her native Pakistan, where last November students at Jamia Hafsa, the mosque’s female seminary, released a video declaring their support for ISIS and asking Pakistani militants to join up with the group. On December 2, around the time of the attack, Malik posted a similar message on Facebook declaring her allegiance to ISIS and its leader, Abu Bakr al-Baghdadi.

All of which to say: Malik and Farook were not “self-radicalized,” they were radicalized by a specific Islamic doctrines that are compelling to millions of Muslims worldwide. The struggle against ISIS is therefore much more than a question of military tactics. It’s a question of ideas, of what the best version of Islam is, or is going to be in the future.

Certain ideas about Islam, after all, led Farook and Malik to stockpile thousands of rounds of ammunition, amass the tools and wherewithal to build pipe bombs, legally purchase semiautomatic rifles, leave behind their infant daughter, and launch an attack on unarmed Americans at a holiday office party. Those ideas can’t be dismissed lightly by political leaders with an agenda; they’re stronger than politics because they strike at the heart of how a person understands the world, God, and the purpose of his life.

Right Now, Muslim Leaders Aren’t Standing Up

Alas, moderate Muslim leaders in America don’t appear to be up for engaging in a war of ideas about their faith. Almost immediately after the attack in San Bernardino, Hussam Ayloush, executive director of the Council on American-Islamic Relations in the greater Los Angeles area, expressed bafflement about the shooters’ possible motives, surmising it could be anything from a workplace grievance to mental illness to some kind of “twisted ideology.”

If moderate Muslims hope to discredit the ‘twisted ideology’ of ISIS among their fellow Muslims, they’ll need to start talking openly about the doctrines and worldview that accompanies it.

He didn’t mention that perhaps Farook and his wife—along with the Pakistani cleric Aziz, Michigan-based cleric Ahmad Musa Jibril, and dozens of Saudi Arabian clerics—support ISIS and believe its version of political Islam is correct. But if moderate Muslims hope to discredit the “twisted ideology” of ISIS among their fellow Muslims, they’ll need to start talking openly about the doctrines and worldview that accompanies it.

They will have to explain, to other Muslims and to a candid world, why political Islam and its various strains of apocalyptic teachings are a thing of the past. They will have to articulate what Islam’s future should be. This will be a generational, global struggle among Muslims—and it won’t be accomplished during the tenure of any one American president.

One might compare what faces Islam today to what Christianity faced in the fourth century in the form of Arianism, a teaching that denied the full divinity of Christ and held that Jesus was not God by nature but a creature susceptible to change. By denying the Trinity and positing a rational relationship between the Father and the Son, Arianism had a certain political appeal for a string of Roman emperors who were more concerned with preserving the unity of the church—and therefore the empire—than with theological distinctions about the nature of Christ.

It would take centuries to purge Christianity of the Arian heresy. At one point, it officially dominated the Roman Empire. But in the end, Trinitarian theology prevailed, in part because Christian leaders knew the Arian teaching that Christ was merely an exalted creature would ultimately destroy the gospel. The opponents of Arianism, in other words, knew they were fighting for the very soul of their religion.

So too with Muslims today. ISIS isn’t just fighting for territory, it’s fighting for Islam’s future. If moderate Muslims have a different and better vision for their religion, they’d better start fighting back.

John is a writer in Austin, Texas. Follow him on Twitter.