A Saudi official opens the door of the Saudi consulate in Istanbul where Saudi journalist Jamal Khashoggi went missing and, according to some Turkish officials, was killed. (Erdem Sahin/EPA-EFE/Shutterstock)

The disappearance and alleged killing last week of dissident Saudi Arabian journalist Jamal Khashoggi while he was visiting the Saudi Consulate in Istanbul is only the latest challenge to a U.S.-Saudi relationship that both governments have diligently cultivated.

The Trump administration has said little beyond expressing public concern over Khashoggi’s fate, and the kingdom has sharply denied any knowledge of his whereabouts. In private, officials from Secretary of State Mike Pompeo on down have been frustrated with the lack of a substantive response to direct high-level queries, according to administration officials.

Confirmation that Khashoggi was killed — as some senior Turkish officials have charged — or even his disappearance at Saudi hands is likely to spark a new round of congressional pressure to reassess the relationship with Riyadh.

“If this deeply disturbing news report is confirmed, the United States & the civilized world must respond strongly, and I will review all options in Senate,” Sen. Marco Rubio (R-Fla.) tweeted Sunday, among a number of similar comments.

Lawmakers on both sides of the aisle, long suspicious of Saudi religious extremism and historic ties to terrorism, more recently have been highly critical of Saudi actions in Yemen and at home. Only last month, they were dissuaded by the administration from stopping U.S. military sales and assistance to the kingdom — the world’s largest purchaser of American defense hardware and a key partner in White House plans to bring Iran to heel and to forge an Israeli-Arab alliance.

Pompeo’s certification that the Saudis were “undertaking demonstrable actions” to reduce civilian casualties in Yemen caused by airstrikes with U.S.-provided weaponry followed an earlier Senate hold on arms sales over the kingdom’s dispute with Qatar, another U.S. ally in the region.

Khashoggi, a prominent Saudi journalist, has been in self-imposed exile for the past year after leaving the country under what he said was fear of arrest. His columns, appearing in The Washington Post and elsewhere, have infuriated the ruling Saudi monarchy, particularly because of his criticism of Crown Prince Mohammed bin Salman, the powerful son of King Salman.

In an early column for The Post last fall, Khashoggi wrote that Prince Mohammed, widely known as MBS, “promised an embrace of social reform. . . .But all I see now is the recent wave of arrests,” he wrote, including of intellectuals and religious leaders who dared to criticize the crown prince.

The Saudis have been a willing recipient of President Trump’s courting, which began in earnest during his first presidential trip overseas, to Riyadh in May 2017. In addition to hailing Salman as a wise and beneficent king of his own people, Trump virtually proclaimed him leader of the Muslim world and America’s closest Arab ally.

The trip also marked a foreign policy shift in which the administration began clearly to equate the purchase of U.S. arms with the pursuit of American policy interests. Since then, Trump rarely meets with a foreign leader — particularly from the Middle East — without publicly raising the subject of American sales of what he has referred to as “lots of beautiful military equipment.”

The apex of that goal so far, however, remains what he touted as $110 billion in Saudi purchases pledged during last year’s visit.

Not all of those deals have yet worked out, however. Despite a 20 percent price cut, the Saudis let a Sept. 30 deadline to lock in the $15 billion purchase of a Terminal High Altitude Area Defense anti-ballistic missile system expire without signing on the dotted line. Administration officials, who spoke on the condition of anonymity about the sensitive U.S.-Saudi relationship, expressed concern that the price for the missiles, manufactured by Lockheed Martin, is now likely to go up, even as U.S. willingness to concede to Saudi-demanded co-production provisions is likely to decrease.

A Saudi official, asked about the deal, said that the kingdom remained “highly interested” in the THAAD system, but “like any military purchase, there are negotiations happening which we hope will conclude in the quickest means possible.”

At the same time, the Saudis have resisted U.S. entreaties to disavow any interest in buying Russia’s S-400 air defense system and have continued talks with Moscow.

Purchase of U.S. defense systems is one component, along with a coordinated stand against Iran and rapprochement with Israel, of Trump administration hopes of drawing the six members of the Persian Gulf Cooperation Council, Egypt and Jordan into what the administration has called a new “Middle East Strategic Alliance.”

A planned summit to solidify the alliance, scheduled for January at Camp David in Maryland, has repeatedly been postponed over the past year as its putative members have questioned its purpose and squabbled among themselves.

“I would characterize the reception as generally accepting the idea in concept,” said retired Gen. Anthony Zinni, the administration’s MESA point man. Zinni toured the region late last month to exchange ideas. “Some are ready to say, ‘Sign me up right now.’ Others, obviously, have a lot of questions,” he said. “No one rejected it outright.”

Some countries would like to see a mutual defense pact, akin to NATO’s Article 5, along with a broad free trade agreement — neither of which the administration is interested in providing. Others, including the administration, would like it to be a vehicle for resolving the dispute with Qatar, but the Saudis and United Arab Emirates staunchly oppose that.

Qatar and Oman are wary of Saudi, UAE and administration aggression against Iran, and all the Arab members worry that the administration harbors plans to use them to solidify a peace deal with Israel against the Palestinians.

“Some weren’t sure this gives them more than they [already] have bilaterally” in their relations with the United States, Zinni said of his recent consultations. “Some are afraid” that it would establish a “first among equals — giving too much to the Saudis,” he said. “Our point was, let’s put it all on the table. We’re not trying to hide anything.”

Confirmation of Saudi responsibility for Khashoggi’s disappearance could complicate efforts to get the alliance off the ground if Congress decides to punish Riyadh and public opinion in the United States demands a response.

Despite their frequent differences, the White House and the Saudis have gone out of their way to present a united front. After Trump insulted Salman at a political rally last week, saying he “might not last two weeks in power” without U.S. protection and calling on Riyadh to “pay for your military,” MBS gently deflected the comments.

“Friends will say good things and bad things,” he said in an interview with Bloomberg published Friday. “You will have some misunderstandings. So we put that in that category.” Trump, he said, was merely making a political statement to “his own people.”

“If you look at the picture overall, you have 99 percent of good things and one bad issue,” the crown prince said. “One percent. I love working with him.”

At the same time, he reminded, far from the United States “protecting” Saudi Arabia, the kingdom has “bought everything with money.”

Kareem Fahim in Istanbul contributed to this report.