WASHINGTON - US President Barack Obama may fail to pacify Gulf Arab fears over his Iran nuclear diplomacy at a summit this week, following a pointed Saudi snub of the event. But a bigger question looms for Washington: how much does it matter?
Obama appears confident Washington has enough leverage to fend off Sunni Arab pressure to do more to stop arch-rival Shi'ite Iran from intervening in conflicts across much of the region, underlining diverging interests between the United States and its long-standing Gulf allies.
By resisting a push by some Gulf Arab nations for new formal security guarantees, for instance, Obama is gambling that the close but often uneasy alliance can weather current differences, especially given long-time Arab reliance on the US military umbrella and advanced weapons supplies.
Obama may be further bolstered by America's increasing energy independence, which has made Gulf oil less critical to the US economy.
"The leverage is much more in Washington than in the Gulf," said Karim Sadjadpour, a senior associate at the Carnegie Endowment for International Peace think tank in Washington and former chief Iran analyst at the International Crisis Group.
Some experts say a new generation of Saudi leaders could respond with further military assertiveness in the Gulf, where the kingdom is currently leading an Arab coalition in Yemen against Iran-allied Houthi rebels. Saudi Arabia and other Gulf states have been important sponsors of the anti-government insurgency in Syria.
Most of the region's ruling Sunni monarchs, including Saudi King Salman, declined to attend the summit, sending lower-level officials in what is seen as a diplomatic snub.
Two of the leaders were never expected to attend due to ill health, and the Saudi government denied that their new king's no-show was intended as a slight.
Still, the absence of many top Arab leaders is seen as a reflection of frustration not only with Obama's engagement with Iran in pursuit of a nuclear deal but over a perceived US failure to support opposition fighters in Syria and to push Israel harder to make peace with Palestinians.
The summit starts with Oval Office talks with the Saudi crown prince and deputy crown prince followed by a leaders dinner on Wednesday and then a full day of talks at Camp David on Thursday. US officials say it will reaffirm a strategic relationship that has served for more than half a century as a cornerstone of US Middle East policy.
US counter-terrorism strategy, they add, continues to rely heavily on co-operation with powerful Arab countries.
But some of the mutual interests that brought them together, such as restraining Iran and a heavy US dependence on Gulf oil, appear to have begun to fray.
Obama initially raised hopes in the region when he announced last month, just after world powers reached a framework agreement with Iran, that he would convene a summit with the Gulf Cooperation Council, made up of Saudi Arabia, Kuwait, Qatar, Bahrain, the United Arab Emirates (UAE) and Oman.
But this week the White House has played down expectations for the outcome of the gathering.
While Gulf officials had signaled a desire for firm new security guarantees, US officials say there will be no actual defence treaty and have cast doubt on the prospect for any kind of new written commitment.
The Obama administration is wary of anything legally binding that could draw the United States into future Middle Eastern conflicts.
Instead, US officials said Obama would offer reassurances mostly in the form of a joint statement and more modest announcements for integrating ballistic missile defence systems, increasing joint military exercises and easing arms deliveries.
In return, the United States hopes that Gulf governments, who are sceptical of any nuclear deal with Iran, will hold off with their criticisms ahead of a June 30 deadline for a final deal under which Iran would agree to restrict its nuclear programme in exchange for relief from crippling sanctions.
Arab complaints, together with fierce Israeli opposition, could make it harder for Obama to win Congress's approval for an Iran deal.
This seems unlikely to satisfy the Gulf states, especially regional power Saudi Arabia. Riyadh believes Washington is not taking seriously enough Iranian support for militias in Lebanon, Syria, Iraq and Yemen, which it says are aggravating sectarian tensions.
The White House says a nuclear-armed Iran would be even more dangerous to its neighbours and this is why the nuclear issue must be tackled first. Tehran denies it is seeking a nuclear weapon.
Marwan Muasher, a former Jordanian foreign minister, said the Obama administration "is not interested in over-indulging" the Gulf states on issues that concern them.
"Are they (the Gulf states) going to go back feeling reassured? I don't think so," he told reporters in Washington.
But the Gulf states may have little recourse but to stick with Washington. Many have spent billions of dollars on US military hardware, rely on American military advisers and have found few reliable partners elsewhere.
Even if Obama sends an implicit message that Gulf countries need the United States more than the United States needs them, he still must address fears that Washington is abandoning them at a time of regional upheaval.
Also, the two sides remain interdependent, militarily and economically.
While a boom in domestic US oil and gas has fed the perception US strategic interests in the region might be on the wane, it has not altered Washington's core strategic interest of secure oil supplies to feed the global market.
"If there were instability in Saudi Arabia this would have great global ramifications," said Brenda Shaffer, an energy security expert at Georgetown University.
And as the Obama administration presses allies like Riyadh to take on a bigger defence burden, the United States continues to stay involved, providing logistical support, for instance, for the Saudi-led campaign in Yemen.