Is China finally coming around on Iran? For years, Beijing's steady backing has helped the Iranian regime frustrate international efforts to isolate and penalize it for its nuclear ambitions. This month, however, there are heartening signs that China is reassessing its longstanding strategic partnership with the Islamic Republic.

China has begun to curtail its energy trade with Tehran, responding to new economic sanctions levied against Iran's central bank by the Obama administration and the increasingly likely prospect of an embargo on Iranian oil by European countries. This month, China's crude imports from Iran have fallen by some 285,000 barrels daily, more than half the total volume China regularly imports from Iran on a day-to-day basis. Chinese officials, moreover, have signaled that this reduction will continue into February and possibly beyond.

This one-two punch to Tehran's economy and nuclear ambitions doubtless has the ayatollahs worried. Iran's economic fortunes are intimately tied to China's rise.

Over the past decade, fueled by massive and sustained economic growth, China has become a ravenous consumer of global energy. By the end of the next decade, according to industry estimates, China's oil consumption could grow by as much as eight million barrels per day, making the Middle Kingdom the world's largest petroleum consumer.

As an engine of Beijing's stunning growth, energy-rich Iran is a natural strategic partner. Three years ago, Iran provided roughly 15% of China's overall oil imports, making it China's second largest oil supplier. Last year, similarly, the Islamic Republic supplied an estimated 12% of China's foreign oil demand.

In exchange for oil, China has been a key enabler of Iran's nuclear ambitions. Beijing turns a blind eye to national firms involved in nuclear commerce with Iran and works diplomatically to dilute international pressure levied by the United Nations and other multilateral institutions. The effects have been dramatic. Knowledgeable nonproliferation experts estimate that a crackdown on those national firms by the Chinese government would effectively cripple Tehran's atomic endeavor, at least in the near term.