For much of the weekend it seemed that the Iranian reformists were set for one of those righteous defeats, in which a united phalanx of state power stands down rioting protesters who must be content that their defiance will lay the groundwork for change not today but at some unknown point in the future. But this morning we awoke to word that Supreme Leader Ayatollah Ali Khamenei has directed the country's Guardian Council to review claims that the election was tainted by fraud. And Mousavi himself reportedly appeared at a rally today in Tehran, his first appearance post-election.

On the face of it, Khamenei could call for a review and then decide that it all checks out and that's the end of it. But it's my experience that that's not how these things play out. When regimes ride these crises out successfully they almost always do so with a united phalanx. You simply do not grant the premise of the critics. Force, much as we like to think otherwise, is often quite efective. (See Tienanmen Square.) Once you do, once you legitimize the premise of the protests, which can quickly shift the momentum of the drama, it's a very slippery slope for the regime.

Perhaps more fundamentally, the people running the regimes aren't idiots. They know the pattern too. And the decision to break the united front, to get into a discussion of the legitimacy of claims against the regime, usually signals internal dissension that is making that united stance unsustainable. In other words, this sort of development is perhaps not a cause of regime weakness but a symptom.

All of which suggests that the next 24 hours will be very consequential. We'll keep watching closely and bringing you the latest. Please keep the links and updates coming.