Saudi Arabian Deputy Crown Prince Mohammed bin Salman in May 2015. (Jacquelyn Martin/Associated Press)

IT ALL began in 1985, when a young leader, groomed within the existing political elite but aware of its flaws, took power amid external threats, societal discontent and lower prices for oil, the state's chief source of revenue. Mikhail Gorbachev launched perestroika thinking he could fix and, ultimately, preserve the Soviet Union. The results proved Machiavelli right: "There is nothing more difficult to take in hand, more perilous to conduct, or more uncertain in its success," he wrote in " The Prince," "than to take the lead in the introduction of a new order of things. Because the innovator has for enemies all those who have done well under the old conditions, and lukewarm defenders in those who may do well under the new."

Now comes a 30-year-old Saudi prince, son of King Salman and the king's third wife, brimming with confidence and promising a sweeping overhaul of the realm, which he explained to high-level U.S. officials during a visit to Washington last week. The issues facing Mohammed bin Salman — rivalry with a rising Iran, which has bred multiple proxy wars; disaffection among youth and women, who chafe at repressive religious strictures; a bloated government overly dependent on volatile oil prices — bear some resemblance to those Mr. Gorbachev confronted. Like Mr. Gorbachev, the deputy crown prince faces opposition, latent for now but potentially furious, from beneficiaries of the status quo. Can he modernize Saudi Arabia without destabilizing it?

Certainly, the prince, whom King Salman has entrusted with the key defense and economic policy portfolios, has bright ideas. His "Vision 2030" would reduce Saudi Arabia's reliance on fluctuating oil revenues in favor of earnings from a planned $2 trillion sovereign wealth fund. Prince Mohammed wants less bureaucracy, more foreign capital, more factories and, above all, more productive work for Saudis, including, he hints, Saudi women. The strategic goal is less vulnerability to the ups and downs of oil markets — and, implicitly, mood swings in the United States, which angered and frightened the Saudis by striking a nuclear deal with Iran.

In his Washington meetings, including one with President Obama, Prince Mohammed emphasized common interests, chiefly the campaign against the Islamic State and other terrorist groups. The truth, alas, is that Saudi Arabia has fallen out of favor with the U.S. public, and much of the U.S. political leadership, for good reason. Not only have Saudis themselves played a murky role in the growth of Islamist extremist ideology over the years; but also fewer Americans think ties to Riyadh justify a blind eye to the Saudis' repressive internal policies, especially the stifling of women's rights.

"Our Vision is a tolerant country with Islam as its constitution and moderation as its method," Prince Mohammed writes in the foreword to Vision 2030. Yet blogger Raif Badawi sits in a Saudi prison, as he has since 2012, having been flogged and jailed for the crime of advocating more tolerance and moderation. "For me," Mr. Badawi wrote, "liberalism simply means, live and let live." Unless and until Prince Mohammed uses his new power to protect and promote the basic freedoms of Mr. Badawi and others like him, even those who wish the Saudi kingdom well may remain skeptical about the promises of change.

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