Mr. Khouri said the Saudi relationship to the United States was more fragile than it looked — he likened it to a “sumo wrestler walking a tightrope.”

“It’s a sign of the times when the Saudi king suddenly has his children in positions for which they have virtually zero qualifications,” Mr. Khouri said, “and Trump is doing the same things. So we’ve got to kind of tighten our seatbelts.”

And Prince Khalid faces undeniable obstacles in Washington.

The young Saudi leadership that he represents has, along with the help of the United States and other allies, propagated an unpopular war that has killed thousands of civilians in Yemen and created a cholera epidemic. The situation has alarmed a bipartisan group of senators, who in June tried to slow down the sale of $500 million in precision-guided munitions to Saudi Arabia. The lawmakers were defeated, but by a slimmer margin than expected.

“At the end of the day, our security is also very important to the United States,” Prince Khalid said, adding that if the sales were stalled, the kingdom would procure weapons “from somewhere else.”

The ambassador is particularly concerned with bipartisan outreach during a volatile time in Washington. Robert Malley, a senior adviser to the Obama administration on the Middle East and now a vice president at the International Crisis Group, who recently met with the ambassador, said the Saudis would need to be careful.

“They need to walk a fine line: Embracing Trump without alienating his foes,” Mr. Malley said in an interview. “Otherwise, they risk losing not just Democrats, but many who are not particularly sympathetic to this administration.”

The regional blockade against Qatar poses another challenge. Prince Khalid made a beeline to Capitol Hill after presenting his credentials to Mr. Trump in July, and met with more than a dozen lawmakers.