One very important thing might change.

Given Obama's expressed determination to act - perhaps even without Congress - Assad would be stupider than usual to use his chemical weapons while negotiations appear to be occurring.

In effect, the "red line" will have been reset.

Will Assad launch another chem attack anyway? Maybe. But now that he's agreed in principle to the Russian response to John Kerry's proposal, he would be taking an even graver risk of Western military action than what he faces now.

Everyone can save face here, if that's what they want to do.

But an offer to negotiate hardly means the end of the crisis, the civil war, or its eventual repercussions.