The decision by King Salman of Saudi Arabia to skip a summit meeting called by President Obama reflects a new reality for two nations that for generations shared goals in the Middle East but that are now at odds in fundamental ways.
Both countries insisted on Monday that the king's absence was not a snub, even as it was hard to ignore four powerful factors that have led to rising tensions between the two nations: the administration's pursuit of a nuclear accord with Iran, the rise of the Islamic State in the region, the regional unrest that came to be known as the Arab Spring and the transformation of world energy markets. An American oil boom in particular has liberated the United States from its dependence on Riyadh and changed a decades-long power dynamic.
To the extent that this week's meetings of Persian Gulf leaders at the White House and Camp David were intended to help smooth over those divisions, an opportunity has slipped away. And the future looks even more complicated if the two countries head down different paths toward their perceived security.
"There's no question there have been differences. That's been true for some time," said Philip Gordon, who stepped down a month ago as the White House coordinator for the Middle East, North Africa and the gulf region. "The relationship is not a sentimental one. We each have interests, and if we show we're willing to work with them on their core interests, they will show they're willing to do that with us."
The question is whether each is willing. In the 70 years since Franklin D. Roosevelt met with King Abdul Aziz, the relationship between the United States and Saudi Arabia has been a complicated marriage of shared interests, clashing values and cynical accommodations. The common denominator was a desire for stability. But now the two sides define that differently.
For Mr. Obama, a diplomatic agreement with Iran curbing its nuclear program offers the strongest chance of keeping conflict in the region from escalating. For the Sunni-led Saudi government, the relaxation of sanctions in the proposed deal would simply give Iran, a predominantly Shiite state, billions of dollars to foment more instability around the region.
While the Americans and the Saudis are now cooperating to fight the Islamic State, Riyadh wants more action to force out the government of President Bashar al-Assad in Syria, while Mr. Obama has been reluctant to intervene. Similarly, while Mr. Obama has portrayed the drive for greater democracy in the region as a force for good, the Saudis see the still simmering Arab Spring movement as a threat to their hold on power.
In the midst of all that, the politics of energy have shifted along with the surge in oil production in North Dakota and Texas. No longer so dependent on foreign crude, the United States can flex muscles without worrying about the Saudis cutting its energy supply. Yet Washington still relies on Riyadh to keep the price of oil low to pressure Russia's energy-based economy in the standoff over Ukraine.
Benjamin J. Rhodes, a deputy national security adviser to Mr. Obama, said that differences were to be expected between two countries with varied interests but that those did not undermine the broader relationship. "We have a very robust agenda that we share with the Saudis," he said. "There have been disagreements under this administration and under the previous administration about certain policies and development in the Middle East, but I think on a set of core interests, we continue to have a common view about what we aim to achieve."
But experts said the United States had little desire to be drawn more deeply into the dangerous proxy war between Iran and the Sunni states playing out in places like Yemen. "The United States is not interested in overindulging in other issues that the gulf states are worried about," said Marwan Muasher, a Jordanian former foreign minister. "Are the gulf states going to go back from this meeting feeling reassured? I would say the answer is no."
Presidents have labored to stay close to Saudi Arabia for decades, but have sometimes run into turbulence. Ronald Reagan sold the Saudis sophisticated Awacs airplanes over the objections of Israel. George Bush sent 500,000 troops to defend Saudi Arabia and reverse Iraq's 1990 invasion of Kuwait. His son George W. Bush shared plans in advance with eager Saudis for his own invasion of Iraq.
But King Abdullah of Saudi Arabia, who died in January, was once so upset with the younger Mr. Bush about his support for Israel that the king threatened to storm out of a visit to the president's Texas ranch. The Saudis also frustrated Mr. Bush by refusing to work closely with the Shiite-led Iraqi government as it fought Sunni insurgents. Over the years, administrations have worried about Saudi money that has financed extremist groups.
Mr. Obama, who ripped up his schedule to fly to Riyadh in January to pay respects to King Salman when he took power, spoke with the king by telephone on Monday. The White House had announced Friday that King Salman would attend the meeting, but was blindsided over the weekend when the Saudis said they would instead send Crown Prince Mohammed bin Nayef and Prince Mohammed bin Salman.
The Saudis said the king needed to stay in Riyadh because of the kingdom's air campaign against Houthi rebels in neighboring Yemen. Some regional experts said that at age 79, he has not traveled much out of the country. But some Arab officials said his decision not to attend reflected a broader disappointment that Mr. Obama would not be offering much concrete security assistance at the meeting.
The king was not the only one to turn down Mr. Obama's invitation. The leaders of Oman, Bahrain and the United Arab Emirates — some of whom are in ill health — will also skip the meeting, sending subordinates instead.
Critics said the list of attendees revealed Mr. Obama's inability to shape events in the region. "It's an indicator of the lack of confidence that the Saudis and others have," Senator John McCain, Republican of Arizona, told MSNBC. He blamed Secretary of State John Kerry for misreading Saudi signals. "He sometimes interprets things as he wants them to be rather than what they really are," Mr. McCain said.
The Obama administration said it had rejected a mutual defense treaty sought by the gulf states several weeks ago. The foreign ministers of those countries, however, raised no major protests to Mr. Kerry when he met with them in Paris on Friday in advance of this week's summit meeting. "There was no hint of dissatisfaction," said Robert Malley, the president's top Middle East adviser.
Adel al-Jubeir, the Saudi foreign minister, insisted on Monday that no slight was intended by the king's last-minute decision to skip the summit meeting. "The idea that this is a snub because the king did not attend is really off base," he told reporters in Washington. "The fact that our crown prince and deputy crown prince attend an event outside of Saudi Arabia at the same time is unprecedented."
White House aides said the Saudi princes were the important ones to deal with on these issues. But the president, who will host a dinner at the White House on Wednesday night and then a day of meetings at Camp David on Thursday, will be left with few prospects for a major breakthrough.
Tamara Cofman Wittes, a former deputy assistant secretary of state under Mr. Obama, said: "If anybody had the idea that the summit, in the midst of everything that's going on, was going to somehow be a neatly wrapped little package that would conclude everything, they were kidding themselves."
Helene Cooper contributed reporting.