Saudi Arabia's King Salman in January. Salman will not be attending a U.S.-Arab summit at Camp David. (Jim Bourg/Reuters)

THE WHITE House may deny it, but the spotty attendance of Persian Gulf leaders at the summit meeting President Obama organized for them this week is an unmistakable signal of dissatisfaction with their U.S. ally. Saudi Arabia’s King Salman is not about to follow the example of Israel’s Benjamin Netanyahu by publicly assailing Mr. Obama’s nuclear negotiations with Iran or his reluctance to counter its aggression across the region. But his decision not to attend a dinner and a day of discussions at Camp David after the White House had already announced his attendance — and the nonappearance of three of the five other heads of state — shows that the administration’s efforts to reassure these long-standing U.S. Middle East allies are falling short.

The cause of the Arabs’ dissastisfaction is not hard to discern. While insisting that he is ready to bolster their defenses and quiet their fears about an emerging U.S.-Iranian detente, Mr. Obama is offering only modest steps: a reiteration of past presidential statements pledging to defend the Gulf states against external attack; a plan to better integrate the region’s missile defenses; more sea and air exercises. What’s not on offer is what the kings and emirs say they want, including a formal defense treaty, sales of high-tech weaponry like the F-35 warplane and greater U.S. support for the forces fighting the Iranians and their proxies in Yemen and Syria.

Mr. Obama is right to resist some of these demands. Congress would surely look askance at a treaty committing the United States to the defense of Doha or arms sales that put Saudi Arabia on a par with Israel. The president ruffled feathers in Riyadh and elsewhere when he made the point in a recent interview that the Gulf states also face “internal threats,” including from their stifling authoritarianism, that rival those from outside; but he was right on that, too. The United States would be unwise to try to balance its engagement with Iran by blindly backing Saudi domestic repression or its rash and unwinnable intervention in Yemen.

But there is a way that Mr. Obama could serve both U.S. interests and those of the Gulf allies: by attacking the Middle East’s most toxic and destabilizing force, the Bashar al-Assad regime in Syria. Syria’s dictatorship is Iran’s closest ally in the region, and its barbarity opened the way for the rise of the Islamic State. Recently, it has suffered battlefield reverses, in part because of increased Gulf aid to rebel forces. If Mr. Obama were to embrace proposals, supported by some senior U.S. officials, to create safe zones in northern and southern Syria for the rebels, the balance could be tipped against Damascus and Tehran — and U.S. allies would have tangible reason to recommit to U.S. leadership.

As it is, this week’s summit appears unlikely to alter a widening gap between the United States and its traditional Mideast allies, which appear to have concluded that they must begin acting to defend their interests without Washington’s help. Reversing that dangerous trend, which could lead to regional war or the nuclearization of the Gulf states, will require Mr. Obama — or perhaps his successor — to demonstrate a willingness to do more about Iranian aggression than convene talks at Camp David.

President Obama gave an overview of issues discussed with Persian Gulf leaders during a meeting held at Camp David Thursday. Obama said the group addressed Iran's nuclear program and the crisis in Yemen, amongst other topics. (AP)