China’s relationship with Russia has only grown closer since Putin’s invasion of Ukraine. Just last month, 2,000 Chinese troops took part in a joint military exercise with Russian forces. That development having already exceeded some of the more pessimistic predictions, the question now is: How close can the relationship get?

Russia is locked in a debilitating war, and its economy is battered by a wave of Western sanctions. Moscow has a thousand reasons to seek better ties with China. But what is China’s motivation?

Russia is no longer the superpower it was in the Cold War era. Its $1.5 trillion GDP is less than that of China’s Guangdong Province ($1.8 trillion). Russia’s economic weakness allows China to view it as less of a threat and more of a junior partner in the global competition with its top rival: the United States.

That said, there are economic reasons to believe that China’s support for Russia will prove unsustainable. After Putin’s invasion of Crimea in 2014, Western countries slapped numerous sanctions on Russia. Moscow turned to China for help in offsetting the sanctions and started to accelerate its de-dollarization efforts. Today, China is far and away Russia’s largest trading partner.

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But while China is economically important for Russia, the converse is not true. Russia accounts for only a small proportion of Chinese trade (2 percent in 2021). Beijing’s trade ties with the U.S. and Europe are much greater (26 percent in 2021), according to Trade Data Monitor.

Despite sharp differences with the West—over human-rights violations in Xinjiang and over the status of Taiwan, to name but two issues—China has proved unwilling to weaken economic ties with the West on Russia’s behalf. Instead, President Xi Jinping has urged the U.S. to lift tariffs on Chinese products. He also hopes to improve relations with several European capitals where China’s wolf-warrior diplomacy has backfired.

More important, China’s leadership fears that creeping too far in bed with Putin might lead to Western financial sanctions on Beijing.

China’s State Administration of Foreign Exchange reports that, as of July 2022, China holds $3.1 trillion of foreign-currency reserves, the largest such holding in the world. China is also the second-largest holder (after Japan) of U.S. Treasury securities, at $968 billion.

Some analysts have argued that China’s significant weight in the global economy protects it from Western sanctions. Nevertheless, Chinese firms are unwilling to risk them, as signaled by their reaction to the war in Ukraine.

For example, since the outbreak of the war, Chinese banks have stopped offering letters of credit for trade with Russia. Chinese energy companies, such as Sinopec, have frozen projects with their Russian counterparts. China’s credit-card processor UnionPay refused to work with Russian banks after Visa and Mastercard stopped servicing them. Even the blacklisted Chinese tech giant Huawei has scaled back its operations in Russia to avoid being sanctioned.

The economic slump caused by China’s strict “zero Covid” restrictions has further complicated Beijing’s efforts to provide long-term economic support to Russia.

To date, China’s assistance to Moscow has been limited to increasing imports of Russian oil and gas and increasing the use of China’s currency in bilateral trade transactions. Neither action is restricted by any international sanctions. However, those efforts have secured only limited benefits for China.

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Certainly, China has benefited from discounted Russian energy exports. Chinese purchases of Russian oil and gas have surged from $20 billion in 2021 to $35 billion since the outbreak of the war earlier this year. However, China will be reluctant to derive too much of its energy supply from any one foreign country, including Russia. Beijing does not want to become so reliant on Russian energy as to give Moscow unwanted political or economic leverage.

Similarly, given Russia’s role as but a minor trade partner, the greater use of renminbi in Russia–China trade transactions is likely to do little to advance the internationalization of the Chinese currency.

More than 40 years ago, the U.S. successfully took advantage of the “Sino–Soviet split” to court Beijing and advance its geopolitical interests. Today, China is not in a position to do the same, simply because access to Western finance, trade, and technology is more important to Beijing and its aspirations than Russia is.

Knowing that Russia relies on a country whose regime survival is strongly linked to the U.S.-led global economy, the U.S. should continue developing tools—including trade sanctions and restrictions on technology transfer—to disincentivize Chinese economic support of Russia.