During the 1991 Gulf War, Saddam Hussein possessed chemical munitions, which he could have loaded into Scud missiles and fired into Israel. Knowing this, James Baker, President George H.W. Bush’s secretary of state, publicly stated that any chemical attack on Israel would be treated in the same way as a nuclear attack on the United States. Saddam must have taken this seriously: He fired many Scuds into Israel during that war, but none of them were tipped with chemical munitions.

Obama hasn’t gone as far as Baker, and it wouldn’t be a good idea to do so, given that he and other world leaders are trying to pressure Iran—one of Syria’s main allies—into halting its own nuclear-weapons program. Nor would it make much sense to attack Syria’s chemical stockpiles: First, their locations aren’t all known; second, blowing them up could scatter the gas for miles around, killing hundreds or thousands of innocent people.

One clear option might be to attack Assad himself or his aides and hideouts (assuming we can track them). There are other, more indirect measures as well, and no doubt some of them are being discussed in the meetings that Secretary of State Hillary Clinton has been holding with top Russian diplomats. The Russians are Assad’s ultimate protectors, yet they are—and always have been—extremely nervous, more so than many U.S. administrations, about letting even the closest allies lay their hands on weapons of mass destruction. Any pressure from Moscow—either the threat of an attack or the act of withholding aid and supplies—could have more effect than anything we could do. (This is another good reason for not turning off that “reset” button in U.S.-Russian relations.)