This summer, Saudi Arabia promised the Trump administration $100 million for American efforts to stabilize areas in Syria. That money landed in American accounts on Tuesday, the same day that Secretary of State Mike Pompeo landed in the Saudi capital, Riyadh, for discussions with the kingdom's leaders about the fate of a missing Saudi dissident. The timing of the money's arrival raised eyebrows even among some of the bureaucrats whose programs will benefit from the influx of cash. "The timing of this is no coincidence," said an American official involved in Syria policy who spoke on condition of anonymity. The disappearance of the Saudi journalist, Jamal Khashoggi, has battered the image of Saudi Arabia and of its powerful crown prince, Mohammed bin Salman, a key player in many of the Trump administration's ambitions for the Middle East. Turkish officials say that Mr. Khashoggi was slain inside the Saudi consulate in Istanbul by Saudi agents on Oct. 2 while he was trying to secure a document he needed to get married. Saudi leaders have denied harming Mr. Khashoggi, but have not provided a credible explanation of what happened to him. Mr. Trump threatened "severe punishment" if it was confirmed that Saudi Arabia killed Mr. Khashoggi. But after speaking with King Salman of Saudi Arabia on Monday, he suggested that "rogue killers" could have been responsible and dispatched Mr. Pompeo to Riyadh to see the Saudi king.