Russian President Vladimir Putin and Chinese President Xi Jinping toast during a signing ceremony on May 21, 2014, in Shanghai. Sasha Mordovets | Getty Images

It's time to start worrying more about what could become the most profound geopolitical shift of the post-Cold War years. China's Xi Jinping and Russia's Vladimir Putin are deepening their two countries' strategic alignment even as long-time democratic allies across the Atlantic grow more distant. Some are going so far as to call it an autocratic alliance. Though it hasn't been (and likely won't be) sanctified by treaty, the Trump administration's escalated pressures on Beijing and continued sanctions on Russia have helped drive the two sides more closely together than at any point since the 1950s. That truth will be on full display next week when President Xi pays a state visit to Russia, their second meeting this year and their 29th since 2013. Xi will attend and speak at the St. Petersburg International Economic Forum, and he'll accept an honorary degree from Saint Petersburg State University. More significant is the underlying Xi-Putin bromance that's spawning a flurry of economic and diplomatic deals even as US-China trade talks run aground. At a press conference this week, Vice Foreign Minister Zhang Hanhui said the two sides are likely to sign joint communiques that will take relations to a new level, following a 24.5 % growth in trade in 2018 to a record $108 billion. Zhang, reflecting Beijing's increased bluntness toward Washington, said the two sides will deal with "outside challenges" and protect each other's security and development. "We firmly oppose the willful use [of] sticks of tariff and protectionism," he said. "Deliberately provoking trade disputes is economic terrorism, economic hegemony and economic chauvinism."

For now, what binds them together is common cause against US global leadership, their shared interest in political survival, their similarly autocratic systems and the personal closeness that has grown between leaders who have acted to concentrate more power in their own hands.

Conventional wisdom has been that the distrust and historic animosities that divide China and Russia are so profound – and the economic and military asymmetries are so great -- that any concerns about a potential alliance that threatens US interests are overdone. "The conventional wisdom no longer applies," write experts Andrea Kendall-Taylor and David Shullman in Foreign Affairs. They argue that the depth of relations between Beijing and Moscow already far exceeds earlier expectations and that "the two countries acting in concert could inflict significant damage on U.S. interests even if they never form an alliance." For now, what binds them together is common cause against US global leadership, their shared interest in political survival, their similarly autocratic systems and the personal closeness that has grown between leaders who have acted to concentrate more power in their own hands. The result is closer cooperation across areas from space navigation and technological development to global diplomacy and intelligence gathering. Thus, it's time for Western leaders to abandon their wait-and-see attitude toward the evolution of Chinese-Russian relations and work out common strategies now to respond to this deepening relationship, counteract its dangers where they arise and provide incentives to both parties not to further align themselves against Western interests. "The alliance, if it becomes concrete, would overturn how we do global politics," writes Bruno Maçães, the former Portuguese Europe Minister, in Politico. "Imagine an international crisis in which Russia and China suddenly emerge as a single bloc…Psychologically, in the mind of the West, it would combine the fear associated with Russia with the apparent invulnerability of China. Washington would feel under attack, Europe, intimidated and unsettled." Adds Maçães: "It would be an entirely new world, and it's one that is coming closer to becoming reality." What previously had put the brakes on deeper Chinese-Russian relations was a combination of Beijing's reluctance to distance itself too much from Washington and Russia's concerns about being overwhelmed, particularly in economic terms, as the junior partner in the relationship. Growing acceptance in Beijing that it is now locked with the US in a decades-long global contest has reduced Chinese resistance to closer relations and increased the attention to exploring areas of common interest. Beyond that, Beijing values Russian military technology and diplomatic sway, even as it accepts Moscow's economic and structural weaknesses.

What's striking is Moscow's rapidly growing acceptance of its role as junior partner in a relationship where not so long ago it was the lead.