How does Russia square its contention that President Bashar al-Assad wasn't responsible for the Aug. 21 chemical-weapons attack, with its agreement that the correct response to that attack is to disarm the Syrian regime of chemical weapons?

And what exactly is Russia's attitude to the "responsibility to protect" principle -- an international duty to prevent the slaughter of civilians in civil wars that was adopted by the United Nations in 2005 -- which Russia says it supports, but tends to block in practice?

At the Valdai Club, a weeklong meeting of Russia watchers held annually on a lake north of Moscow, a top Russian diplomat heavily involved in the negotiations over Syria made a capable attempt at squaring the two circles (he's very good). The discussion took place under so-called Chatham House rules, which allow him to be quoted, but not by name.

On the chemical weapons question, the official said Russia wants to remove them from Syria to prevent them from falling into the hands of terrorists, who, according to him, make up at least 75 percent of the rebel forces. Asked (by a Russian participant) if he hadn't just said the rebels already had the weapons because they were responsible for the attack, the diplomat didn't skip a beat.

He said the recent finding in a UN report on the attack on the Damascus suburb of Ghouta last month that sarin gas was delivered by Soviet-era rockets indicates nothing. The rockets identified in the report, he said through a translator, were manufactured from the 1950s to the 1960s, often under license in other ex-Soviet bloc countries, and were distributed to "40, 50 or 60" different countries -- including Libya. Thanks to Western intervention, he said, arms from Libya were now spread across the Middle East.

Second, the chemical warhead was made "in a garage" and fixed onto the rocket, which is primarily used with conventional munitions. "These are all homemade weapons," the diplomat said. "If we allow industrially produced chemical weapons to reach the hands of the opposition that would be terrible." He was convincing. As I said, he's that good.

The diplomat wasn't asked about the UN report's inclusion of directional coordinates, which allowed Human Rights Watch among others to track the launch point of the rockets to the main base of Assad's most loyal unit in Damascus.

Russia's leaders may or may not believe their story, yet they have little choice but to stick with it. If they don't, they will have to acknowledge that Assad is a war criminal; accept that the UN Security Council resolution under negotiation should identify Assad as the culprit of the Ghouta attack; and either mount an argument that a mass-murdering war criminal shouldn't be touched, or agree to authorize his punishment by force should he refuse to give up the weapons. That isn't going to happen -- it opens the door to regime change.

There's even an argument to made that Russia should stick to its story. If the UN resolution identifies Assad as a war criminal, there is a good chance he won't agree to any deal or future settlement because his brightest future then would be as a prisoner of the International Criminal Court in The Hague. The diplomat stressed that Russia has less influence over Assad than is often assumed in the West (they were much better friends with Assad's father, Hafez, he said, whereas Bashar has proved slippery, cozying up to the Europeans until he needed Russia's help again).

The determination to block any form of military intervention leads directly to the second unsquared circle: Russia's approach to the responsibility to protect, which mandates the protection of civilians. Russian leaders hate R2P. They see it (with some justification, see Libya) as a charter for the U.S. and its allies to topple autocrats they don't like. The potential implications for dictators in ex-Soviet republics in Central Asia and in Belarus are clear.

The diplomat explained the broader Russian thinking behind the Syria talks -- to revive international diplomacy within the constraints of the law, meaning the UN Security Council, where Russia has a veto. To his credit, the diplomat did volunteer the link to R2P, which he acknowledged was a UN-approved principle.

At the same time, though, he said repeatedly that there has never been an example of military intervention that made things better -- he pointed to Iraq (no argument there); Libya (open to debate, but he has a case); and Afghanistan (I'd argue that one, but hardly fatal to his point).

Bosnia, however, is indisputable. The 1995 intervention, which was backed by Russia and the Security Council, ended years of slaughter. The diplomat didn't mention it. Nor did he mention the 1999 Kosovo intervention, where Russia blocked action through the Security Council, and the North Atlantic Treaty Organization acted anyway. Nor did he bring up Rwanda, where hundreds of thousands of civilians died without any outside intervention, and a reminder that failure to act can also make things worse.

So Russia believes that external military intervention (presumably with the exception of Russia's involvement in Georgia in 2008) is always bad, but at the same time it supports the responsibility to protect civilians in civil wars. "We would not like concepts such as responsibility to protect to degrade into a right to punish," he said. The argument needs work.

(Marc Champion is a Bloomberg View editorial board member. Follow him on Twitter.)