For more than a year, there have been persistent reports of weapons crossing the border to help the Syrian resistance and evidence of co-operation between Syrian and Iraqi jihadists. Resupply convoys headed through Iraq to the Syrian regime have been ambushed in recent months.
In the view of Ian Bremmer, president of the Eurasia Group, "Iraq is teetering back towards civil war, with direct implications for the investment climate across the country, and deepening geopolitical conflict between Iran and the Sunni monarchies" of the Gulf.
Turkey is also growing alarmed at the prospect of a more "Balkanized" Syria. It already has 322,000 refugees on its soil, according to latest figures from the UNHCR, the U.N. refugee agency, with another 100,000 clamoring to cross.
Turkish Prime Minister Recep Tayyip Erdogan has upped his rhetoric in recent days, criticizing the Israeli strikes but reserving his most passionate denunciation for the Assad regime.
"You, Bashar Assad, will pay for this. You will pay heavily, very heavily for showing courage you can't show to others, to babies with pacifiers in their mouths," he told an audience over the weekend.
But Erdogan is struggling to turn indignation into influence. As the International Crisis Group noted in March: Turkey "now has an uncontrollable, fractured, radicalized no-man's-land on its doorstep."
The Jordanians know how that feels. They are trying to cope with 450,000 Syrian refugees -- equivalent to some 7% of the Jordanian population -- growing restless and desperate in makeshift camps. The number in Lebanon has shot up to 455,000, according to the United Nations. In all, the Syrian conflict has generated an extra half million refugees in just two months.
Lebanon -- whose sectarian equation mirrors that in Syria -- cannot help but be dragged into the war next door. Several Salafist sheikhs in Lebanon have declared jihad against the Syrian regime in response to Hezbollah's growing involvement. One of them, Sheikh Ahmed Assir, called on Sunnis in the city of Sidon to form brigades to help the resistance in Qusayr. And rocket fire, apparently from the Free Syrian Army, has landed in Shiite areas around the Lebanese town of Hermel.
A land of bad options
Some critics of the Obama administration say there is a moral imperative to intervene in Syria in the face of slaughter (at least 70,000 Syrians have died so far.) In the Washington Post, former Obama adviser Anne Marie Slaughter has recalled the "shameful" failure to confront genocide in Rwanda.
But Cordesman writes: "Syria has become the land of bad options. The Obama administration has reason to hesitate in intervening."
And Joshua Landis, who runs the blog Syria Comment and is director of the Center for Middle East Studies at the University of Oklahoma, warns that even "a humanitarian intervention will become a nation-building project, as was the case in Iraq."
With the number of internally displaced now put at 4.25 million people, that would be a huge project.
The dream among diplomats a year ago was that a moderate opposition could be brought together with some regime elements to ease al-Assad from power. As the Syrian war threatens to become a regional one, the United States and Russia are dusting off that option, calling for an international conference within weeks that would be attended by both the government and the opposition.
"The alternative is that Syria heads closer to the abyss, if not over the abyss and into chaos," said U.S. Secretary of State John Kerry.