Last week, Mr. Trump announced that he would be pulling American forces out of Syria almost immediately, despite a previous declaration that troops would be there indefinitely. Advisers persuaded the president to delay the withdrawal for a few months. By Monday, he was hinting at a sudden escalation of force after another suspected chemical attack in Syria by its leader, President Bashar al-Assad.

“We are meeting with our military and everybody else, and we’ll be making some major decisions over the next 24 to 48 hours,” Mr. Trump said on Monday morning. A chemical attack, he said, “can’t be allowed to happen.”

Confusion over the Trump administration’s regional policy goals has led a caravan of Middle Eastern leaders to come to Washington to lobby directly for their interests. Three weeks ago, Crown Prince Mohammed bin Salman of Saudi Arabia was hosted at the White House and then toured the United States; he headed home this past weekend, after a reunion with Presidents George Bush and George W. Bush.

Now, Mr. Al-Thani will get his moment.

“The visit of His Highness will showcase the strength and honesty that exists between the U.S. and Qatar,” said Jassim Al-Thani, a spokesman for Qatar’s embassy in Washington.

The Trump administration had hoped to bring all of the leaders of the Gulf Cooperation Council together for a summit meeting in Washington this month. But Prince Mohammed of Saudi Arabia and leaders of the United Arab Emirates said they would decline such an invitation were it issued, since such a meeting would have required an end to their Qatar embargo, senior administration officials said.

Jon B. Alterman, a senior vice president at the Center for Strategic and International Studies, said the growing disarray in the Middle East was in some ways reflected and grows out of a chaotic White House.

“How do you pursue a coordinated interagency U.S. government strategy when the U.S. government isn’t coordinating?” Mr. Alterman asked, citing the absence of ambassadors in Saudi Arabia, the Emirates and Qatar and dozens of other countries along with vacancies in Washington.