Following the downing of a suspected Chinese spy balloon by a US fighter jet last month, President Joe Biden stated that he planned to speak with Chinese President Xi Jinping about the incident in order to clear the air between the rival superpowers.

The call has still not been made five weeks later.

Instead, after two months of diplomatic squabbling and Xi’s visit to Moscow this week, where he and Russian President Vladimir Putin jointly denounced the United States, US-China relations have deteriorated to what some say is the worst since the countries normalized relations in the 1970s.

Further complicating matters are stopovers in the United States next week and in early April by Taiwan’s President Tsai Ing-wen, who according to sources familiar with the planning may meet Republican House Speaker Kevin McCarthy during a “transit” stop in California on her way back from Latin America.

“This is not a good moment for American diplomacy,” said William Kirby, a professor of Chinese studies at Harvard University. “The last time China and Russia were this close was 1957, when Mao Zedong declared in Moscow, ‘The East Wind will prevail over the West Wind.'”

Now U.S. officials are once again asking how to reset the world’s most important bilateral relationship.

A Biden-Xi call would be an obvious first step. But despite the efforts of U.S. diplomats, sources said the Chinese have shown little interest in committing to such a call, which would be their first known interaction since a November meeting at the G20 in Bali.

Blinken did meet with China’s top diplomat Wang Yi at the Munich Security Conference last month after the balloon incident, but this did not soothe tensions. A source familiar with that conversation called it the most antagonistic U.S.-China engagement since contentious talks in Alaska early in the Biden administration.

The person said China had declined to coordinate the meeting, forcing the State Department’s top East Asia diplomat, Daniel Kritenbrink, to personally track down Wang Yi at the conference center to ask whether it would happen.