As Turkey threatens reprisals for bombings that have left up to 50 dead, Syria's war is already sucking in the wider Middle East. But the one country on which all sides would previously rely for leadership is paralysed with indecision.
The most striking aspect of the Syrian imbroglio, as I have discovered on a visit to neighbouring Lebanon, is that this may be the first conflict of the post-superpower era. The United States does not know what it wants. And even if it did, it seems fearful to use the means at its disposal to engineer it.
A year ago, when I was last in Beirut, people said Syria's president, Bashar al-Assad, had, perhaps, three months to hang on; now he looks much more entrenched. Militarily, the regime has consolidated its precarious hold on Damascus and other key cities. Rebel forces are increasingly desperate and disparate – and fears are growing that the al-Qaida-inspired al-Nusra Front is the only organised element. Some diplomats say that the Assad regime deliberately stokes these fears, but admit that they add to a sense that Syria is a lose-lose for everyone involved.
In his re-election inaugural address in January, President Obama insisted that a decade of war was coming to an end. Afghanistan and, particularly, Iraq have set back the cause of humanitarian intervention for at least a generation. Libya was seen as a modest operation, with modest success, but even that has been undermined by the murder in Benghazi by jihadists of the US ambassador to Libya, which has been ruthlessly and opportunistically taken up by the American right.
For Obama, therefore, the option of cutting his losses and keeping his distance from Syria has proved attractive. The problem is that his government will not admit this to be strategy, providing false hope to the self-proclaimed moderate opposition and its Sunni supporters in Turkey, Qatar and the region.
America's reluctance has prompted Israel to step into the breach. Its massive air strikes on targets in and around Damascus on 5 May were designed to send a message not just to Assad but also to Hezbollah and, most of all, Iran. The Israelis are clear about what they don't want – the shipment of heavy weaponry to Hezbollah in southern Lebanon.
Yet do the Israelis want Assad to stay or go? Nobody in Beirut or elsewhere in the region appears to know the answer. To paraphrase Franklin Roosevelt's depiction of the Nicaraguan leader Anastasio Somoza: "He may be a sonofabitch, but he's our sonofabitch." Israel has been relatively comfortable with the Assad dynasty, which has kept a lid on the occupied Golan Heights – just as they appreciated Hosni Mubarak's ability to keep Egyptians in check.
Both Israelis and Americans would do anything to lessen Iran's influence over Syria. Their game plan – if one exists – might approximate to: get rid of Assad, put someone in place who would maintain order, allow moderates in the opposition a stake in government, be a little more friendly to the west, and keep the Iranians and Hezbollah at arm's length. Do all this by discreetly supporting those rebel elements you're not too squeamish about.
Suffice to say such an intricate non-plan as this has virtually no chance. In the meantime, more than 70,000 have died, and the war is spilling over Syria's borders, as the weekend's attacks on the Turkish town of Reyhanli attest. Lebanon, a fragile state of only 4 million, is attempting to absorb a million refugees from Syria. Pro- and anti-Assad fighters cross the porous border every day. With the prospect of a sectarian conflagration inside Lebanon growing all the time, a report by the International Crisis Group describes the situation as at breaking point.
The absence of leadership or strategy is palpable. On Assad's use of chemical weapons, which Obama said would mark a red line, it appears that the US bluff may have been called. In another sign of the west's weakness, both David Cameron and the US secretary of state, John Kerry, have gone cap in hand to Assad's chief supporter, Vladimir Putin – a few months ago the Americans and British were dismissive of the Russian position. In their meeting in Washington on Monday, Cameron said he and Obama – "whatever our differences" – had the same aim as Putin: "a stable, inclusive and peaceful Syria free from the scourge of extremists". That statement meant everything and nothing.
Twenty-five years of single-power dominance came crashing down with Iraq. Obama has been wise and politically brave to shed the hubris and self-delusion that had taken hold. Libya was a brief interlude, but the days of heavy-handed military intervention are over. It is Syria's tragedy, and will soon be others', that nothing has been put in its place.
John Kampfner is a former chief executive of Index on Censorship.