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Congress is expected to vote this week on giving the Obama administration the authority to combat the Islamic State in Iraq and Syria by providing arms and training—to someone. But whom?

Even assuming President Obama gets the authority he wants, experts say deciding who exactly should get American aid is an exceedingly difficult task. There are vast differences among Syrian rebel fighters—a conglomerate of varying ideologies, social backgrounds, and loyalties. And the questions of who exactly is a Syrian moderate, and whether these weapons will fall into the wrong hands, loom large on Capitol Hill.

"As you know, in the Middle East, it's very difficult to predict what's going to happen," Rep. Jack Kingston of Georgia said after emerging from a closed-door House GOP conference meeting Thursday. "And that's why everybody wants to be very careful about this because we do have concerns about that."

There isn't a formal definition of a Syrian moderate, said Leila Hilal of the New America Foundation. But implicit in the word, she says, are a few criteria: a Syrian who is a nationalist and is fighting for a secular, democratic, and inclusive state.

That definition leaves a lot of room, Hilal said, and there are ample rebel fighters on the ground. Previously, the Syrian National Coalition could have used its Supreme Military Council to help determine who is a moderate, she said. But that group has essentially been disbanded, and now determining who exactly fits the "moderate" bill is done on an ad hoc basis.

"One of the problems is that whether or not someone is fighting under an Islamic banner or a Syrian revolutionary flag, they're often working together on different fronts," said Hilal, a senior fellow with New America's International Security Program. "If they're fighting to take over the military base or airport "¦ different groups ideologically predisposed will be fighting together."

A political framework is key, she said, rather than handpicking rebels to do the fighting.

"In my mind, in order to mount an effective counterterrorism strategy, you really need a robust nationalist force that isn't just a select group of so-called moderates."

Some lawmakers, such as GOP Rep. Michele Bachmann of Minnesota, said the president is picking the wrong people to fight this war.

"What would giving more money and more weapons to these guys do?" Bachmann said Thursday. "It would build up ISIS. It wouldn't defeat ISIS, it would build them up because the so-called vetted moderates, our supposed good guys, wouldn't be fighting the enemy. I think what would happen is we would end up funding the enemy."

Before the U.S. chooses whom to equip and train, a background check is performed. The Department of Defense works closely with the intelligence community, using all of its databases in the vetting process, according to Commander Elissa Smith, a Pentagon spokeswoman. She declined to further detail the process, but said it involves appropriate agencies and departments.

This is "vitally important" as there are concerns that the weapons could fall into the wrong hands, said Rep. Michael McCaul, the House Homeland Security Committee chairman, after an all-member classified briefing Thursday. And while there isn't 100-percent assurance that this won't happen, there's a "high degree of confidence" in the vetting process, which the Texas Republican said has progressed in recent years.

But background checks aren't what concern Michael O'Hanlon, the director of research for the Brookings Institution's Foreign Policy program. Rather, it's the capacity for the U.S. to talk to tribal elders who can vouch for a fighter, mentor units once formed, and then continue to monitor their behavior.

There should be some basic guidelines, such as ensuring there isn't a connection to terrorist groups, said O'Hanlon, who is also a senior fellow with the Center for 21st Century Security and Intelligence at the Brookings Institution. "Half the point is to create the moderation," he said. "You don't presume the moderation, you build it."

And then, you monitor it. But unlike in Afghanistan and Iraq, there aren't thousands of American troops in Syria who could do that. And this, O'Hanlon said, takes a large step out of a multipronged process.

It's inevitable that some skeptics will remain, especially on Capitol Hill.

As House Appropriations Chairman Harold Rogers put it last week: "They use the term 'moderates.' I don't know a moderate person in Syria. "¦ We've seen arms that we supplied in Iraq and Afghanistan, American arms, now in the hands of fighters in Syria."

This article is from the archive of our partner National Journal.

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