A tone of desperation pervades President Putin’s appeal to his “dear friend” Xi Jinping, the president of China, in the face of their common foes.

“Russians are feeling increasingly alone,” a senior fellow at the Carnegie Endowment, Alexander Gabuev, writes in Foreign Affairs. “Putin’s decision to invade Ukraine has forced Russia to turn to its fellow Eurasian giant, hat in hand.”

Indeed, Mr. Putin in a video chat with Mr. Xi was almost begging him to come to Moscow by “next spring” —  after that harsh Russian winter — for a state visit. Mr. Putin no doubt is already planning a grandiose welcome, after which he’ll be pleading for his friend to aid Russian troops mired in what looks like an unwinnable war in Ukraine. 

Just as carefully, Mr. Xi is telling Mr. Putin, not so fast. His measured response, in their video conversation, carried by China Global TV, was evident when he praised Russia for having never refused to resolve the conflict through diplomatic negotiations. 

M. Xi even engaged in some old Cold War-style rhetoric, pontificating that “containment and suppression are unpopular, and sanctions and interference are doomed to failure.” Moreover, he said,  throwing in more cliches, China stands “ready to work with Russia and all progressive forces” against “hegemonism and power politics.”

What Mr. Xi clearly did not say was that China would support Russia in Ukraine. The degree to which China will go along with Russia may depend on Moscow’s willingness to provide the right enticements. An increased supply of natural gas from a newly opened field in Siberia would help. 

Mr. Putin left no doubt of his urgent need for Chinese assistance, calling specifically for “cooperation between the armed forces of Russia and China” in the interests of “the security of our countries and maintaining stability in key regions.” 

If Mr. Xi is not excited about Ukraine, he definitely looks to Russia as a partner in China’s expanding military role in Asia. Russian and Chinese warplanes have engaged of late in intimidating war games in which they have intruded into the “air defense identification zones” of South Korea, Japan, and Taiwan, and both of them support the North Korean strongman against South Korea and its ally, America.

China is not quite ready, however,  to view America, South Korea, or even Japan — which took over portions of China in the 1930s — as total enemies. An overriding consideration is the tremendous trade and investment that China enjoys with all of them. 

Then, too, lurking in the background, is that Chinese-Russian relations have had deep downs along with steep ups. There was a time, after Mao Zedong’s Red Army triumphed over the Chinese mainland in 1949, that China and the Soviet Union, both firmly Communist, got along fine.

“In the twentieth century, the Soviet Union viewed China — at least until the Sino-Soviet split of the 1960s — as a poorer cousin, a country to be steered and helped,” Mr. Gabuev writes. That was before Mao and Joseph Stalin fell out with one another and their troops began firing sporadically across their common frontiers.

Now the table is turned. China looks like Russia’s big brother: sometimes helpful, sometimes not.  For Messrs. Xi and Putin,  the enemy of my enemy is my friend — as long as Russia pours in ever more natural gas, the major source of Russia’s income.