STEVE INSKEEP, HOST:
The U.S. is carrying out two types of military action in Syria. One is airstrikes, and the other is training and arming 5,000 moderate Syrian rebels.
RACHEL MARTIN, HOST:
And while there's some debate about whether the president had the authority to order the airstrikes without approval from Congress, it turns out the arm and train mission may be on shakier legal grounds.
INSKEEP: That effort is supposed to help rebels fight the group that calls itself the Islamic State. Those same rebels also want to topple the Syrian regime led by Bashar al-Assad. And the prospect of overthrowing a government is where the legal questions come in. NPR's David Welna reports.
DAVID WELNA, BYLINE: Hours after Congress voted to arm the Syrian rebels, President Obama called that plan a key element in the United States strategy against ISIL, the term he uses for the Islamic State.
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PRESIDENT BARACK OBAMA: With this new effort, we'll provide training and equipment to help them grow stronger and take on ISIL terrorists inside Syria.
WELNA: But in that same statement, Obama also acknowledged that the rebels the U.S. would help do have more than one enemy.
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OBAMA: These Syrian opposition forces are fighting both the brutality of ISIL terrorists and the tyranny of the Assad regime.
WELNA: And because those Syrian fighters aimed to overthrow Assad, giving them military aid might further that cause, too. New York University law professor Ryan Goodman runs the national security blog Just Security. He says, the US aid for Syrian rebels could easily be turned against Assad.
RYAN GOODMAN: One doesn't have to think about arming them. It's even an easier point to make that training the rebels to make them a more effective war-fighting group - there's no way you could say, OK, you know, only use that effectiveness against ISIL, but not against Assad.
WELNA: Which is why Goodman and other legal experts say, the U.S. could be violating international norms that ban one nation from attacking another. Arming Syria's rebels, he says, reminds him of the U.S. training and equipping the Central American rebels known as Contras during the Reagan administration.
GOODMAN: It's very similar. I mean, Reagan, you know, at the time, in the 1980s, referred to those as moderate forces in the democratic resistance to Nicaragua.
WELNA: The International Court of Justice ruled the U.S. violated international law by helping the Contras go after Nicaragua's Sandinista regime. But that law, which is part of the United Nations charter, makes an exception for self-defense. University of Virginia law professor Ashley Deeks says, that exception allows the U.S. offensive against Islamic State insurgents.
ASHLEY DEEKS: So if you did use force against ISIS, under collective self-defense, I think it's perfectly justifiable to arm rebels who are fighting ISIS. Where it gets a little bit more complicated is where there's rebels maybe fighting multiple groups, including ISIS, but maybe also including Assad's government.
WELNA: Syrian officials have not objected to U.S. airstrikes against the Assad regime's enemy, the Islamic State, but what they have objected to is the aid to rebels approved by Congress.
WALID AL-MOUALEM: (Through translator) What we have witnessed on the the part of the U.S. administration is a practice of double standards.
WELNA: Speaking through an interpreter last week at the UN General Assembly, Syrian Deputy Prime Minister Walid Al-Moualem said, it was clear why the U.S. was arming Syrian rebels.
AL-MOUALEM: (Through translator) To score certain political agendas, particularly through supporting them with money, weapons and training for these groups that they call the moderate.
WELNA: Whether the training and arming of Syrian rebels is legal may come down to a simple question - what is the U.S. really trying to do? Massachusetts House Dem. Jim McGovern voted against that aid. He did so, he says, because too little is known about America's aims in Syria.
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REPRESENTATIVE JIM MCGOVERN: It's not really clear whether the real goal is simply to go after ISIL or whether, ultimately, the goal is to go after Assad. The real intent here, I think, to whether or not it's a violation of international law.
WELNA: But it will take months to decide which rebels receive aid, which means it could be a long time before America's real intent becomes clear. David Welna, NPR News, Washington. Transcript provided by NPR, Copyright NPR.