First he ordered the detention of at least four senior members of his own royal family. The next day he plunged Saudi Arabia into a price war with Russia that sent energy and stock markets around the world into free fall.

For a while, Crown Prince Mohammed bin Salman of Saudi Arabia had appeared to be living down his reputation for dangerous aggression.

Perhaps chastened by the blowback over his connection with the killing of the dissident journalist Jamal Khashoggi, the 34-year-old crown prince had kept a low profile for more than a year.

Now his new power plays are reviving debates in Western capitals about whether he is too rash to trust as a partner. His sudden, steep cut to the price of oil has rocked a global economy already at risk of falling into recession, threatened to burn through Saudi Arabia’s cash reserves and undermined his grandiose promises of new investments to lessen the kingdom’s dependence on oil.