Sen. Bernie Sanders wants Iran and Saudi Arabia to send ground troops into Syria as part of a coalition of Muslim nations to fight ISIS, an idea he’s pressed multiple times as a strategy to fight Islamic extremism in the region.

It’s the Middle East policy equivalent of a COEXIST bumper sticker. Sanders’s proposal might sound promising to a foreign policy lightweight—but those with expertise in the area know that the concept is deeply troubling.

“These comments indicate Sanders’ lack of serious engagement with foreign policy issues. While I appreciate his opposition to the Iraq War, perhaps if he was a little more engaged with that issue he would understand the problematic elements [of his proposal],” said Evan Barrett, a political adviser to the Coalition for a Democratic Syria, a Syrian-American opposition umbrella group.

Sanders has preferred to stick to economic issues, an environment that he is deeply familiar with. But he has been apparently unprepared to address national security topics, a primary responsibility of the commander-in-chief position he is seeking. His puzzling comments on how to fight ISIS are just the latest manifestation of his lack of foreign policy fundamentals.

Running against former Secretary of State Hillary Clinton, Sanders was always going to be on the defensive when it came to foreign policy expertise. But the Vermont senator isn’t doing himself any favors when he consistently argues for a leading state sponsor of terrorism to team up with its mortal adversary to fight ISIS, an extremist group which Iran’s own actions are empowering.

Sanders has repeatedly said the United States should not take the lead in the fight against ISIS. But the unserious part of his proposal is the suggestion that he suggests Saudi Arabia and Iran should work together to fight Islamic extremism—seemingly oblivious to the schisms in the region.

“We have to understand that the Muslim nations in the region—Saudi Arabia, Iran, Turkey, Jordan—all of these nations, they’re going to have to get their hands dirty, their boots on the ground. They are going to have to take on ISIS. This is a war for the soul of Islam,” said Sanders at the Democratic presidential primary debate in November.

But that wasn’t just an off the cuff gaffe. It’s a point the Vermont senator has repeated in press releases for the past year: The war against ISIS, he said, “must be won primarily by nations in the region—Saudi Arabia, Turkey, Qatar, Kuwait, Jordan and Iran— which must be prepared to send ground troops into action to defeat Islamic extremists.”

Sanders’s campaign did not respond to requests to clarify the senator’s strategy on ISIS.

The first problem with Sanders’s proposal is the Vermont senator doesn’t seem to recognize that there is serious animus between certain Muslim countries: Saudi Arabia and Iran are deeply at odds, and have been for quite some time.

In fact, many Sunni states in the Middle East view Iran’s growing regional power as a challenge rivaling that of ISIS itself—many American partners in the region, such as Saudi Arabia and Qatar, would refuse to cooperate with Iran, since they believe that Iranian aggression in Iraq, Syria, and Yemen is contributing to the sectarianism that fuels ISIS.

“Sanders does not understand that Sunni nations are as concerned—if not more—about Iranian hegemonic goals as they are with the threat of ISIS,” said Michael Pregent, an adjunct fellow at the Hudson Institute and a former intelligence adviser to Gen. David Petraeus on Iranian malign influence.

The most recent flare-up of this tension occurred this month after predominantly-Sunni Saudi Arabia executed a prominent Shiite cleric, Sheikh Nimr al-Nimr. When Iranians responded by storming the Saudi embassy in Tehran, the Saudis cut off diplomatic ties with their rivals.

“In an environment where Saudi Arabia and Iran are consistently at each other’s throats in multiple regional theaters, a presidential candidate with limited interest in foreign policy insisting that they work together because they are both Muslim is deeply troubling and suggests grave ignorance,” Barrett said.

Both countries are suspected of backing rival armed factions in Syria—meaning that Iran and Saudi Arabia arguably already have troops in Syria, in the form of proxy fighters that have prolonged the war and the suffering endured by the Syrian people.

Sanders also doesn’t seem to realize that Iran already has combat forces in Syria—and they have been a disaster for Syrian civilians, and are arguably pushing more of them towards ISIS.

“Iran already has troops in Syria and they aren’t fighting ISIS. They are providing an advisory and officer position level role for informal militias and Hezbollah troops conducting operations against U.S.-backed rebels… and carrying out ethnic cleansing of Sunnis in regime strongholds,” Barrett told The Daily Beast. “All these practices push Sunni communities towards ISIS and other extremist groups.”

Despite the nuclear accord reached between the United States and Iran, it remains on the State Sponsors of Terrorism list, designated by the State Department to have repeatedly provided support for international terrorism. But Sanders said that he wants Iran, among other countries, to take a leading role against ISIS.

“The U.S. and the international community should be fully supportive, but the leadership in this war must come from the Muslim world,” Sanders said in September 2014.

Pregent says that he’s alarmed that Sanders would cede regional leadership to Iran.

“Sanders’s statements portend that he would outsource U.S. foreign policy in the Middle East to Iran,” Pregent said. “Iran is not in Iraq and Syria to defeat ISIS—they are there to grow influence and ensure their proxies are emboldened and empowered.”