AMMAN, Jordan — As next in line to be king of Saudi Arabia, Mohammed bin Nayef was unaccustomed to being told what to do. Then, one night in June, he was summoned to a palace in Mecca, held against his will and pressured for hours to give up his claim to the throne.

By dawn, he had given in, and Saudi Arabia woke to the news that it had a new crown prince: the king’s 31-year-old son, Mohammed bin Salman.

The young prince’s supporters have lauded his elevation as the seamless empowerment of an ambitious leader. But since he was promoted on June 21, indications have emerged that Mohammed bin Salman plotted the ouster and that the transition was rockier than has been publicly portrayed, according to current and former United States officials and associates of the royal family.

To strengthen support for the sudden change in the line of succession, some senior princes were told that Mohammed bin Nayef was unfit to be king because of a drug problem, according to an associate of the royal family.

The decision to oust Mohammed bin Nayef and some of his closest colleagues has spread concern among counterterrorism officials in the United States who saw their most trusted Saudi contacts disappear and have struggled to build new relationships. And the collection of so much power by one young royal, Prince Mohammed bin Salman, has unsettled a royal family long guided by consensus and deference to elders.

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