Proponents of the U.N. Arms Trade Treaty (ATT) assert that the treaty prevents signatories from supporting not only the Syrian opposition but future rebellions against other totalitarian regimes.

The Geneva Academy argues that the transfer of arms to a non-state actor “could amount to a violation” of the treaty. At Oxford University, Stuart Casey-Maslen states that the ATT makes transfers “arguably…unlawful.” David Bosco at Foreign Policy calls British support for arming the Syrian rebels “possibly contradictory” given Britain’s backing for the ATT. Rachel Stohl, an influential U.N. consultant on the ATT, opposes aid to the rebels (though not specifically because of the ATT). And Control Arms, the umbrella nongovernmental organization (NGO) backing the ATT, asserts that the war in Syria is “stark proof that [the ATT] is needed to stop weapons exacerbating already horrific abuses against civilians.”

The Administration disagrees with this interpretation of the treaty. Assistant Secretary of State Thomas Countryman has asserted that “I can’t say that if the ATT were enforced today for the United States that this issue [of Syria] would be any easier or any harder than it already is.” The ATT clearly does not absolutely ban the transfer of arms to a non-state actor: If it did so, the ATT would have won the support of more nations in the U.N. General Assembly, and the treaty supporters would not condition their arguments with “could amount to” and “arguably.” But the pro-treaty forces appear to agree that, in the words of Scott Stedjan, Oxfam America’s senior policy adviser for humanitarian response, “the treaty goes further than what the U.S. currently does and what it says…and over time…it will have an effect on U.S. practice.”

As Stedjan’s comment implies, enthusiasm for the ATT is in part an effort to turn a policy dispute into a legal question and so transform U.S. foreign policy by raising treaty-based arguments against it. But the treaty advocates are making two arguments: a broader one that the ATT bans aid to all rebel groups and a narrower one that aid to the Syrian rebels is against the rules.

The broader argument is significant if, as they concede, far from bulletproof. But the Syrian case is also important, both on its own and for what it tells us about how the treaty advocates will look at future cases. Here, for two reasons, the treaty advocates have a stronger, though not perfect, argument.

First, the ATT states that one of its objects is to “prevent and eradicate the illicit trade in conventional arms.” From a legal point of view—though not a common-sense one—the Syrian regime is responsible for determining what trade to Syria is legal. The treaty thus appears to oblige signatories not to engage in trade to Syria that the regime brands as illegal, and the regime certainly rejects efforts to arm rebels that seek to overthrow it. As German Chancellor Angela Merkel said last week, “Germany has very clear legal rules that we do not send weapons into civil wars.”

Second, the ATT imposes a number of prohibitions and tests on arms shipments, and it is far from clear that the rebels meet (or that any group of rebels could meet) the treaty’s human rights standards, even taking into account that under the treaty the risk of human rights violations must be “overriding.” Reports that elements of the Free Syrian Army have massacred Christian villagers outside Homs will only raise new doubts on this score.

There are indeed good reasons to be skeptical about arming the rebels in Syria. But by arguing the broader case that the ATT bans aid to non-state actors, the treaty proponents are rejecting a bipartisan tool of U.S. foreign policy, one that we may not want to use now but should not abandon. They are validating the concerns of treaty opponents, who have long argued that the ATT was a device to transform U.S. arms export policy. They are also effectively putting themselves on the side of the well-armed totalitarian regimes that kill unarmed people.

And there is a final irony. The ATT is being promoted by an Administration that is seemingly intent, in Syria, on seeing the treaty their way. Other governments are likely to do the same, which implies that the ATT—to the extent that it does not over time constrain the U.S., as its advocates argue it should and will—is likely to achieve nothing at all.