Chinese President Xi Jinping and U.S. Secretary of State Rex Tillerson in Beijing on March 19. (Thomas Peter/Associated Press)

If President Trump goes through with an expected summit with Chinese President Xi Jinping at Mar-a-lago next week, the United States’ allies in Northeast Asia will be watching closely to see if the Trump administration will stand by its friends against increasing pressure from Beijing. How Trump deals with China’s massive retaliation against South Korea in response to U.S. missile defense deployment is one crucial test.

Secretary of State Rex Tillerson reinforced the Trump administration’s commitment to deploy the THAAD missile defense system in South Korea during his trip there this month. Standing next to the South Korean foreign minister, he sent a not-so-subtle message to Beijing that the deployment is not about China and will go forward over Chinese objections.

What Tillerson didn’t say was whether the U.S. government is concerned about the Chinese government’s multifaceted campaign of intimidation and punishment of a host of South Korean government and business entities as part of a campaign to pressure the South Korean leadership to walk away from its decision to deploy THAAD.

With a changeover in government coming to Seoul soon that could see a much more China-friendly leadership take power, the Chinese intimidation campaign is ramping up and the United States has largely remained silent. Republican lawmakers in both chambers of the U.S. Congress are calling on the Trump administration to do more.

“The Chinese are trying to use this moment to rattle the nerves of an incoming administration in South Korea. If there’s any time that we need to protect our ally, it’s now,” Cory Gardner (R-Colo.), chairman of the Senate Foreign Relations subcommittee on Asia, told me. “THAAD is an incredibly important part of strengthening our alliance and showing our commitment to our alliance with South Korea.”

In the House of Representatives, Trump ally Ted Yoho (R-Fla.) introduced a resolution last week calling on the Chinese government to cease its “unreasonable and inappropriate retaliatory measures against the Republic of Korea, its businesses and its people in an attempt to halt the deployment of THAAD.”

The resolution, which was marked up in the House Armed Services Committee on Wednesday, calls on the U.S. government to take all available measures to protect its ally. Yoho told me that the Trump-Xi summit is a perfect time for the president to raise this issue with the Chinese leadership.

“You’ve got to bring this stuff to the table,” Yoho said. “Our goal is to protect our 28,000 troops in South Korea and protect the Korean people.”

The scope and pace of Chinese retaliation against South Korea related to the THAAD deployment has been accelerating in recent months and spans the governmental, economic, commercial, aviation and tourism sectors.

The most visible example of Chinese retaliation has been against the Lotte Group, one of South Korea’s largest foreign retail operators. Lotte agreed to a land swap with the South Korean government to facilitate THAAD deployment. Subsequently, there have been protests in China against Lotte, operations at 39 retail stores in China have been suspended, and the Chinese government has begun a comprehensive tax probe into Lotte’s China operations.

China’s Global Times wrote this month that unless Lotte changes its mind, “the determination of Chinese society to make it pay the price for its decision to support to host the THAAD would be firm too.”

Chinese retaliation extends to many other areas. Performances by South Korean musicians in China have been abruptly canceled. K-pop music and Korean soap operas have been removed from Chinese media platforms. No Korean films are allowed  at the upcoming Beijing film festival.

Chinese tourist agencies are reportedly no longer offering visits to South Korea, and China has banned charter flights to South Korea during the peak travel season. Chinese tactics have severely damaged South Korea’s cosmetics industry, which has new trouble getting goods into China.

China has also restricted South Korean military and diplomatic exchanges, for example by canceling a South Korean minister’s invitation to an annual forum and denying entry to China of a South Korea Navy ship last December. China has also begin flying military planes in the South Korea’s air defense identification zone without prior notice, a provocative and dangerous tactic.

Typically, Beijing denies that it is perpetrating a coordinated pressure campaign against South Korea over THAAD. But in January, Chinese Foreign Minister Wang Yi tipped Beijing’s hand when he said, “The Chinese government will make efforts to resolve this conflict if the deployment is put on hold.”

To many in Washington, China’s actions contradict Xi’s promise to pursue free trade and also his commitment to stand with the international community to do everything possible to counter the threat of North Korean missiles.

“China has done all of this to stop the deployment of a missile defense system, which is only necessary because China has aided and abetted North Korea for decades,” Senate Armed Services Committee Chairman John McCain (R-Ariz.) said in a January statement.

Whether the Trump administration stands up for South Korea, especially during next week’s summit with Xi, will send a clear signal to all Asian allies about whether or not the United States is as committed to their security as before.