Lithuania, a Baltic state of 2.8 million with an outsize role in promoting human rights and democracy, is in the crosshairs of Russia and China. Neither Russian President Vladimir Putin nor Chinese leader Xi Jinping has been shy about going after Lithuania. But their recent moves have broader significance, namely testing American and European commitments to allies.

Mr. Putin is raising the temperature on Lithuania by absorbing neighboring Belarus into his security sphere and militarizing Kaliningrad, Russia’s territorial exclave...

Illustration: David Klein

Lithuania, a Baltic state of 2.8 million with an outsize role in promoting human rights and democracy, is in the crosshairs of Russia and China. Neither Russian President Vladimir Putin nor Chinese leader Xi Jinping has been shy about going after Lithuania. But their recent moves have broader significance, namely testing American and European commitments to allies.

Mr. Putin is raising the temperature on Lithuania by absorbing neighboring Belarus into his security sphere and militarizing Kaliningrad, Russia’s territorial exclave on the Baltic Sea. Mr. Xi is waging a campaign of political and economic retaliation.

The integration of the Baltic states into the North Atlantic Treaty Organization and the European Union in 2004 was a crowning achievement of post-Cold War politics. Lithuania helped lead Europe’s response to the depredations of the dictatorial regime of Alexander Lukashenko in Belarus by sheltering opposition leaders and staking out hawkish positions. This is the latest way in which Vilnius has irritated Mr. Putin, who would like to reclaim Russia’s near abroad as a sphere of influence. In Mr. Putin’s fanciful telling, Lithuania is a major source of Russia’s historical insecurity. That places it high on the list of neighboring states he would like to control.

Lithuania drew China’s fury this year for its decision to leave the 17+1 format—the Beijing-designed framework for dealing with Europe—and by allowing the government of Taiwan to open an office for its representation in Vilnius. Beijing declared an import ban on products with goods made in Lithuania—a move damaging to European companies with factories or supply-chain sources in Lithuania. Continental, a Germany-based automotive supplier, is the latest multinational under Chinese pressure to close operations in Lithuania.

The question is how closely Russia and China will be willing or able to cooperate. In the China-Russia best-case scenario, the EU fails to support Lithuania and EU companies look elsewhere to source goods for the Chinese market. Meanwhile, Mr. Putin impinges, perhaps indirectly, on Lithuanian territory, sovereignty or independence—in the name of ensuring Kaliningrad’s security—and encounters no effective U.S., European and NATO response.

As Mr. Xi knows, if he and Mr. Putin successfully detach Vilnius from NATO and the EU, there would be immediate ramifications in Asia, where China wants to push the U.S. out and establish regional hegemony. Most military strategists identify Taiwan as China’s best first target for confrontation—and thus the essential test of U.S. resolve. But an indirect opening move in the “gray zone” of conflict aimed at Lithuania might have advantages.

If the U.S. and Europe fail to back Lithuania fully, America’s allies and partners in Asia will doubt U.S. commitment. Rather than working closely with Washington, they might become more friendly with China. Sun Tzu would smile at winning the battle for Taiwan in Lithuania.

He also would admire Mr. Xi’s ability to get Mr. Putin to do the dirty work of testing the depth of U.S. alliance commitments in Asia. This surrogate arrangement has two advantages. First, it exposes Mr. Putin to most of the risks, such as sanctions. Second, it cements a strategic partnership between China and Russia in which Mr. Putin’s Russia assumes the role of junior partner to the far more powerful China.

After Russia annexed Crimea in 2014, NATO deployed four multinational battalion-size battle groups in the Baltic States and Poland as part of the so-called enhanced Forward Presence mission. For its part, the EU is considering trade measures following China’s boycott of Lithuania to defend member states against economic attacks. These steps are worthy but not enough to check such determined foes as Messrs. Putin and Xi.

The West too often relies on outdated policy tools. In response to China’s boycott of Lithuania, Brussels has pointed to the World Trade Organization as the best place for relief. In military matters, enhanced Forward Presence is a rotational rather than permanent NATO force of limited size and power. Neither the WTO nor enhanced Forward Presence is enough to guarantee Vilnius’s independence.

Lithuanian Foreign Minister Gabrielius Landsbergis recently described his country as a “canary in the coal mine.” America’s allies and partners around the world will study the U.S. commitment before choosing their own paths. As Vilnius feels the heft of Russian and Chinese power, U.S. and European credibility is on the line, in the form of an alliance guarantee. To back down under pressure would prove disastrous for Lithuania, and for the West’s global reputation.

Messrs. Lindberg and Rough are senior fellows at the Hudson Institute.

Journal Editorial Report: After the Afghan debacle, Xi and Putin are on the move. Images: AFP/Getty Images/Shutterstock Composite: Mark Kelly The Wall Street Journal Interactive Edition