“You need Saudi Arabia to be at the center of this coalition,” said Daniel B. Shapiro, a former United States ambassador to Israel. “Right now, it’s unlikely you would find any member of Congress or western European leader willing to sit with the crown prince for consultation.”

On Monday, the Turkish drip of well-aimed leaks about the Khashoggi case escalated with the revelation that after he was killed in the Saudi Consulate in Istanbul, the Saudis sent out a body double dressed in Mr. Khashoggi’s clothes as a decoy. The news raised new doubts about the Saudi explanation that Mr. Khashoggi was killed accidentally in a fistfight, suggesting instead a premeditated plan to eliminate him.

Saudi Arabia’s shifting responses to the accusations have hindered its efforts to contain the story. And as each new Turkish revelation has undercut the latest Saudi explanation, the cumulative effect has been a severe blow to the reputation of the kingdom and of Prince Mohammed, known by his initials as M.B.S.

Lasting damage to Saudi Arabia’s standing could ripple across the region, affecting conflicts from Libya to Yemen while making it harder for the Trump administration to press for a peace deal in the Holy Land and build a multilateral alliance against Iran, two of its key goals for the Middle East.

“What we are seeing in the region are expressions of loyalty to Saudi Arabia, but they mask real concerns among Saudi Arabia’s close allies about the viability of the current regime and about how its behavior is going to affect the region,” said Lina Khatib, the head of the Middle East and North Africa program at Chatham House.