WASHINGTON — For America’s top diplomat, it will be a mission like no other: seeking to build a coalition among U.S. allies against Iran, while also defending a potentially historic disengagement of Washington from the Middle East.

Starting this week, Secretary of State Michael R. Pompeo will swing through at least eight countries in eight days, including Egypt, Saudi Arabia and most of the Persian Gulf, in a bid to portray “America as a force for good in the region,” a senior State Department official said.

His is one of two high-level U.S. officials’ trips to the region since President Trump abruptly announced the withdrawal of American troops from Syria on Dec. 19. As Pompeo heads to Arab capitals, a parallel mission has Trump’s national security advisor, John Bolton, traveling to Israel and Turkey. Trump himself spent about 3½ hours on a U.S. air base near Baghdad visiting American troops the day after Christmas.

The withdrawal from Syria, which Trump ordered against the advice of aides and without warning allies, alarmed both Israel and the United States’ Persian Gulf allies who, under U.S. urging, have taken steps to unite in a “maximum pressure” campaign against Iran.

The removal of Ameri-can forces is likely to improve Iran’s position and ease the way for the Islamic Republic to expand the influence of the militia groups it backs to within striking distance of Israel’s border, U.S. and foreign experts agree.

Other likely beneficiaries of a U.S. withdrawal are Russia and Syrian President Bashar Assad, whose removal from power was a principal goal of Western involvement in Syria’s eight-year civil war.

Trump seemed to cement his intention to disengage from the region when he said that Iranians can “do what they want” in Syria, as far as he was concerned, describing Syria as a country of “sand and death.”

Critics from both political parties, as well as former and current diplomats and officials, said such comments underlined Trump’s propensity for making bold, robust claims, but then not showing a willingness to back them up, or do the work and make the investment necessary to achieve them.

Trump is trying to achieve “maximalist objectives with minimal investment,” said Colin Kahl, an international security expert at Stanford University and former Obama administration official, citing Trump’s desire to hold Iran in check even as he scales back U.S. power in the region.

That complicates Pompeo’s mission to explain U.S. intentions and reassure allies about the U.S. commitment to challenge Iran.

“The United States is not leaving the Middle East,” a senior State Department official said, calling such suggestions “false narratives.”

“We are not going anywhere.... The policy of maximum pressure on Iran has not changed,” said the official, one of several who briefed reporters ahead of Pompeo’s trip, which starts Monday, under rules requiring anonymity.

The administration’s recent actions, however, and especially those of Trump, have invited skepticism.

“I don’t see how any foreign government or leader can believe anything said by any of Trump’s subordinates,” said Charles Stevenson, an associate director of the foreign policy program at the Johns Hopkins School of Advanced International Studies.

Trump “is missing opportunities to lead,” Stevenson added, “and disengaging to the point that others are acting ... to determine the narrative.”

Trump’s desire to disentangle the United States from conflicts overseas, along with his disdain for multilateral institutions like the United Nations and for international treaties that he has abandoned, is in step with his broader doctrine of “America first.” Administration officials have repeatedly denied the slogan means “America alone,” but their denials have been needed because many foreign officials — as well as domestic critics — see it as precisely that.

The approach is at its most stark in the Middle East, where for the seven decades following World War II, U.S. policy has been relatively consistent in seeking to be the region’s dominant outside influence, favoring Israel, but also, in fits and starts, bent on finding a peaceful solution to the Arab-Israeli conflict and an independent state for a generation of displaced Palestinians.

“The days of American dominance in the Middle East are over,” Martin Indyk, a senior State Department official in Democratic and Republican administrations, said on Twitter shortly after Trump’s announcement. “All hail Putin, Erdogan (and Khameini),” said Indyk, a two-time U.S. ambassador to Israel.

He was referring to those who are seen to have most benefited from Trump’s withdrawal decision: Russian President Vladimir Putin; Turkish President Recep Tayyip Erdogan, who is eager to attack U.S.-backed Kurdish fighters in Syria; and Iran’s supreme leader, Ali Khamenei.

Others who have been supportive of many of Trump’s policies and who are hawkish on Iran are also concerned that the Islamic Republic could readily step in to fill the void left by a U.S. withdrawal from Syria, as well as the president’s plans to sharply reduce the number of American troops in Afghanistan.

“During a time in the Middle East when Iranian resolve is on the rise, the U.S. appears to be slinking away, drawing down troops, closing consulates, and removing missile defenses,” said Behnam Ben Taleblu, a research fellow at the Foundation for Defense of Democracies, a conservative advocacy organization in Washington.

“This sends all the wrong messages to Iran, and worse, to U.S. partners in the region like Israel and the GCC,” he said, referring to the six-nation Gulf Cooperation Council.

Taleblu and others praised the administration’s reimposition of tough economic sanctions on Iran. The sanctions had been lifted by President Obama as part of the 2015 international Iran nuclear deal and were reinstated last year when Trump unilaterally withdrew from that accord. But, they said, the sanctions do not go far enough in pressuring Tehran.

State Department officials, however, insisted that the “maximum pressure” campaign continues at full force and has had a punishing effect on the Iranian government and its economy. Sanctions have targeted individual Iranian leaders and military men as well as state companies, Iran’s central bank and numerous third-country parties who attempt to deal with Iran.

“Our military position may be changing, but our overall goals remain the same,” the official said.

Pompeo’s trip marks his second to Saudi Arabia since the Oct. 2 killing of U.S.-based Saudi journalist Jamal Khashoggi, which the CIA concluded was orchestrated by Saudi Crown Prince Mohammed bin Salman, a favorite of the Trump inner circle who is also the de facto ruler of the desert kingdom.

In the first trip to Riyadh, two weeks after Khashoggi was slain inside the Saudi Consulate in Istanbul, Turkey, news photos showed Pompeo laughing and shaking hands with the crown prince, without a word of condemnation. Since then and to much outside criticism, Trump and Pompeo have indicated they accepted official Saudi explanations that the crown prince was not involved in the gruesome slaying.

State Department officials said Friday that they were not convinced by official Saudi accounts — a departure from previous statements. The official version, that Khashoggi was killed by a rogue government hit squad gone wrong, has not “yet hit the threshold of credibility and accountability,” one of the State Department officials said.

Regardless, Trump’s high regard for the crown prince, as well as his decision to leave Syria, have had the effect of shoring up autocrats in the region, analysts say.

The crown prince, something of a pariah in much of the world after the Khashoggi killing, has consolidated his power. Assad, not long ago on the ropes and facing his demise, is winning his war, with Russia’s help, and is now being welcomed back into the bosom of the Arab world.

And Egypt’s President Abdel Fattah Sisi, a brutal abuser of human rights, according to numerous independent accounts, is also in the good graces of Trump, who has shown much affinity for those to whom democracy is not necessarily a top priority.

On his second stop, the State Department official said, Pompeo will meet with Sisi in Cairo to reinforce “one of our longest-standing, deepest and broadest partnerships.”

tracy.wilkinson@latimes.com

Twitter: @TracyKWilkinson