US and Saudis seek common ground
Washington will remember the first visit of Saudi Arabia's King Salman for its royal extravagance.
The massive fleet of luxury cars for the hundreds of officials who accompanied the monarch. The full buy-out of the 222-room Four Seasons Hotel, reportedly outfitted with red carpets and gold-painted furniture for the occasion.
But the message the US and Saudi leaders wanted to send was one of a resilient relationship.
"Strong", "deep" and "abiding" were some of the words they used.
Rhetoric aside, it was clear the Saudis had decided to move beyond deep reservations about the Iran nuclear deal which have strained relations with the Obama administration in recent months.
At the height of tensions in May, the king refused President Obama's invitation to visit, although the Saudis insisted it wasn't a snub.
Since then, negotiations on the deal have concluded successfully and, perhaps recognising a fait accompli, Riyadh expressed cautious support.
But Foreign Minister Adel al-Jubeir now gave ringing endorsement. After consulting US officials and European allies for two months, the Saudis were satisfied, he said, that the agreement would effectively contain Iran's nuclear programme.
They now had "one less problem to deal with in regards to Iran".
So President Obama got what he wanted: strong public support from a crucial ally, and at a critical time - just as a hostile Congress is preparing to vote on the deal.
This may help to silence those who blamed his foreign policy for losing the trust of key Middle East powers.
The focus can now turn to what the Kingdom considers the main problem - rolling back expanding Iranian intervention in the region.
Saudi Arabia and other Sunni Arab states feel threatened by Iran's support for Shia groups in Mid-East conflicts: Iraqi militias; the regime of Bashar al-Assad in Syria; the militant Hezbollah movement in Lebanon; and Houthi rebels in Yemen.
And the fear is that lifting sanctions on Iran according to the terms of the nuclear deal will embolden it further.
This was an abiding theme at a recent conference on US-Islamic relations in Doha. So much so that the senior White House official attending, Colin Kahl, felt compelled to clarify that although the US stood by its Gulf Arab partners, "this can't be a competition to the death with Iran".
The Obama administration insists it will help the Arabs counter Iran's "destabilising activities". It's offering to strengthen measures for facing unconventional threats from Iran's proxies, including cyber and maritime security, and increased counter terrorism co-operation.
Despite this emphasis on "more nimble 21st Century capabilities", conventional sales of military hardware haven't slowed. New Saudi purchases are in the process of being approved and President Obama has promised to fast track what's in the pipeline.
The Gulf Arab states are also looking for US guarantees of a "qualitative military edge over Iran", says James Smith, a former US ambassador to Saudi Arabia. It's not clear if King Salman got that.
Yemen and Syria
Mr Obama and the Saudi monarch talked about two other areas of co-operation and disagreement as well.
In Yemen, the Americans are supporting the Saudi-backed campaign against Houthi rebels. But they are appalled at the resulting humanitarian disaster and high number of civilian casualties. The meeting ended with Saudi Arabia pledging to work towards opening Red Sea ports for aid deliveries under UN supervision.
In Syria, the two co-ordinate against Islamic State militants but disagree about how to approach the broader civil war - the US is uneasy about Saudi willingness to back certain hardline Islamist fighters, and the Saudis want Americans to directly target Mr Assad's government.
They're both participating in a new flurry of diplomatic activity aimed at reviving a political solution, but Mr al-Jubair said a breakthrough wasn't imminent.
These complex problems in the new chaos of the Middle East need a level of strategic dialogue not previously necessary, says Anthony Cordesman, a Middle East analyst at the Center for Strategic and International Studies think-tank.
"Alliances with Arab states are going to have to adapt to events that none of us can control," he says, and that includes Iran's behaviour.
"If this agreement is the prelude to a more moderate Iran, the strains on the (Saudi) alliance will ease because the need to take tangible action will be reduced. But there's never going to be complete agreement on how to deal with Iran short of a major war."
Two very different countries will have to find ways to co-operate with each contingency and "that is not going to be easy".