Ties That Bind Putin and Xi Tested by Russia’s Ukraine Invasion

They visited a hockey rink in Beijing and the panda enclosure at the Moscow Zoo. They shared blinis layered with caviar in Russia and, reciprocally, the popular variant in China, jianbing. They have shared birthday cakes and exchanged toasts with shots of vodka, while demurring that neither would dare go overboard with the stuff.

For more than a decade, Xi Jinping of China and Vladimir V. Putin of Russia have forged a respectful, perhaps even warm relationship, reflecting the deepening ties between two world powers that share common cause against American military and economic might.

The invasion of Ukraine could upend all that — or forge, in diplomatic isolation, an alliance that reshapes the world order in the 21st century.

Three days into the conflict, it seemed clear on Sunday that Mr. Putin’s expectation of a quick subjugation of Ukraine was foundering. Ukrainian resistance slowed or stalled Russia’s forces, while Western nations sharply escalated economic pressure on Russia, which was looking almost totally isolated.

Mr. Putin’s attack on Ukraine has forced Mr. Xi into what Kevin Rudd, the Australian ex-prime minister who was once a diplomat in Beijing, called an “impossible balancing act” between his personal camaraderie with the Russian leader and the potential for blowback for China, should it be seen as endorsing an invasion condemned by most of the world.

On Friday, Mr. Xi spoke by telephone with the man he called his “best friend” in 2019, but stopped far short of endorsing the assault on Ukraine. He said all countries should “abandon a Cold War mentality,” and he expressed support when Mr. Putin told him he would seek a negotiated resolution to the war, according to the Chinese government’s summary of the call.

But there is no sign that Mr. Xi did anything to ward off the invasion, if he knew it was coming. His senior advisers rebuffed American requests to use China’s influence with Mr. Putin to discourage an attack; instead, China shared the Americans’ intelligence with the Russians and accused the United States of trying to sow discord, according to American officials.

For China, the costs of Mr. Putin’s adventurism could be high.

“I don’t think this is good for anybody,” said Wang Huiyao, president of the Center for China and Globalization, a research organization in Beijing that advises the government. “Conflict is not a solution, and China doesn’t want to see things deteriorate.”

China has deep ties with Europe and the United States that it cannot afford to sever, despite growing tensions in those relationships. The Ukraine invasion has rattled Chinese stock markets and threatens to roil the global economy during an important political year for Beijing that is expected to end with an extension of Mr. Xi’s rule.

The international furor over Ukraine — and the diplomatic isolation Mr. Putin is expected to face — could also serve as a warning of what Mr. Xi can expect if he uses force to subdue Taiwan, the self-governing democracy that China claims as its territory.

Mr. Putin, for his part, appears to be banking on China’s support over Ukraine — explicit or not — in the face of…