If Plan A fails in Syria, what is Plan B? The question was raised last week by Kofi Annan, the sponsor of the UN and Arab League "ceasefire" plan, when he asked the General Assembly: "What other options exist to address the crisis?" The question must be answered. With another UN official declaring this week that Syria is already in a state of civil war, attention must turn to possible alternatives to the Annan plan.
This does not mean the time for talking is over. Diplomatic and economic pressure can still bite; Russia might yet be persuaded, by appealing to its interests, to pressure President Bashar Al Assad to step down - while he still can. Elements within the regime might do the same.
But the window for a negotiated solution is closing; reports that Russia is supplying the regime with attack helicopters is a grim portent for the violence ahead.
The best chance for an end to the bloodshed remains defections from Mr Al Assad's inner circle or from the armed forces. If the merchant class in Aleppo and Damascus can be persuaded to come out openly against Mr Al Assad, as some are increasingly doing, that could swiftly end his regime.
Continued pressure on the economy could prove decisive. Syria released new banknotes into circulation yesterday, potentially increasing inflation rates already running at 30 per cent. And yet the massacres - in Houla, in Al Qubair, in Al Haffeh and elsewhere - mean that simply biding time will soon cease to be an option. The international community must begin to prepare for that eventuality.
Military escalation is fraught with dangers. The rebels lack the training and weaponry to fight the regime's planes and tanks. But arming them could set up an insurgency that could last years, with no definitive result. Moreover, intervention, such as in Libya, could provoke a regional conflict. Groups in Syria would likely splinter and Lebanon might be drawn in; the Assads are well known for stoking regional tensions for domestic gain.
Another solution might be humanitarian buffer zones on the border with Turkey, as advocated by France and others. But this option would require an international commitment - and a military component - that entails many of the same risks.
Every military solution is bad. A civil war under the current circumstances would be long, bloody and regionally destructive. The best hope is that Syrians will force a solution - the decision is in the hands of the opposition and, unfortunately, the remaining regime loyalists. The Assad regime will fall. When and how remain open questions.