Events are moving very quickly now. But the latest developments are that Syria has publicly admitted for the first time to harboring chemical weapons, has agreed to reveal its stockpiles, and has indicated it will sign the international convention banning chemical weapons.

Various reports indicate that sticking points remain, such as the U.S.’s demand for a binding United Nations resolution requiring Syria’s complicity, and Russia’s demand that the U.S. officially renounce force as part of any compromise.

However, Gary Samore, Obama’s former White House coordinator for arms control and weapons of mass destruction, tells me he’s skeptical both of the possibility of a deal being reached — and of it being successfully implemented.

Samore — who was Obama’s WMD coordinator from 2009 until earlier this year — says he thinks Obama is doing the right thing in trying for such a deal, but that the differences between the U.S. and Russia may be unbridgeable.

“There are some very fundamental differences between a deal we could accept as the basis for disarming Syria, and a deal Russians are prepared to agree to,” Samore says. “If we want to execute this idea in a meaningful way, you need a binding UN Security Resolution under Chapter 7 authority — you want the threat of force as a requirement, not optional. The fact that the Russians are not willing to support that is a pretty bad indication that they will not go along with a deal that we would require to be confident we can achieve the objective of disarming Syria.”

Samore said a deal that might be acceptable to the U.S. would require Syria to join the Chemical Weapons Convention, and then agree to have its weapons destroyed under international monitoring by the Organization for the Prohibition of Chemical Weapons. But “if it doesn’t have behind it the threat of force, then it’s a pretty weak resolution,” Samore adds.

However, Samore doubts that the Russians would accept this, unless there were “built into the resolution a requirement that any use of force to implement the resolution would require an additional action by the UN Security Council, which would give the Russians a veto.”

Yet there is an outside route to a deal, Samore says. The U.S. could accept a general comromise such as the above, while declining to “accept the argument that we could only use military force later if it is approved by the UN Security Council.” At the same time, the Russians might accept such a deal — one that doesn’t include the U.S. agreeing to take force off the table later — as “a better alternative to the U.S. bombing of Syria.”

Of course, that puts us back where we started, with Obama possibly having to act unilaterally later. Since Congress may be unwilling to authorize that, the President could, in this scenario, end up acting alone without Congressional support.

Samore says that the bottom line here is that, for all the conservative claims that Russia is playing the United States in this process, Russia is offering to broker some kind of deal because it is eager to avoid U.S. strikes on Syria.”The reason we’re at this point, without a doubt, is because of the Russian desire to avoid an American attack on Syria,” Samore says. “From the Russian standpoint, the U.S. has been going around unilaterally destroying Russian clients. All of that demonstrates Russian impotence.” He cited Iraq and Libya as examples.

And for that reason, Obama should keep trying, because common ground is feasible. “In a funny way, both have a common interest here,” Samore says. “Both sides want to avoid an attack on Syria.”

But even if a deal is reached, it could be very hard to implement. “These kinds of disarmament agreements are very difficult to exercise under normal conditions,” he says. “You would expect Assad to declare a portion of his chemical weapons and try to squirrel away a portion. Assad and his government have a very strong interest in hanging on to their chemical weapons. They believe they’ve been effective in the civil war and also believe they give protection against external military attacks.”

“So you would need a pretty intrusive verification mechanism, which means visiting a lot of sites and interviewing a lot of people,” Samore concludes. “Doing this in the middle of a civil war? Who’s going to protect the inspectors? Are you going to send in a UN-authorized military force to defend them? The destruction could take years.”