A cat near a building covered in hundreds of posters of Chinese President Xi Jinping in Shanghai on Saturday. (Aly Song/Reuters)

AS CHINESE President Xi Jinping visits Washington this week, a kind of guerrilla war is underway between his repressive security apparatus and what appears to be a growing legion of critics. It’s a lopsided contest: Journalists and other activists who dare to challenge the Communist leader for his concentration of power and assault on dissent quickly disappear. Those outside the country risk abduction or the arrest of family members in China. And yet, the resistance continues, driven by Mr. Xi’s own excesses.

The latest flare-up concerns the appearance of a letter demanding Mr. Xi’s resignation on an official website on March 4. Attributed to “loyal Communist Party members,” the missive accused Mr. Xi of “indulgence in a personality cult” and quashing critics in a way reminiscent of the Cultural Revolution. “Our Party, our country and our people can not afford another 10 years of turmoil,” it said.

While the authors of the letter are unknown, it likely reflects the reviews of many inside and outside the Chinese establishment. After two decades in which the ruling party drifted toward a collective system of leadership, and pressure rose for open debate and the rule of law, Mr. Xi has moved aggressively against journalists, lawyers and academics pushing for liberalization. While his Maoist tactics are shocking, the visible pushback they have engendered is even more remarkable. The letter followed bold public statements by a business tycoon and several other critical editorials and blog posts in Chinese media.

The regime’s response has been harsh. According to the BBC, as many as 16 employees of the website that posted the letter have been detained by authorities. In addition, an independent journalist linked to the site disappeared while attempting to board a flight to Hong Kong. Two Chinese writers based in the United States and Germany have reported that their relatives in China have been arrested as a way of pressuring them to reveal what they know about the document.

The attempt to blackmail critics outside the country ought to particularly concern the United States and other Western governments. Wen Yunchao, the New York-based blogger whose parents and brother were arrested, rightly accused the authorities of kidnapping; he said they knew he had not written the letter but were trying to force him to disclose any information he had about its distribution. Chang Ping, the writer based in Germany, gave a similar account, saying his two brothers and a sister had been taken away.

Mr. Xi appears confident he will suffer no consequences for these obvious violations of international law, or for the abduction of other critics in Hong Kong and Thailand — including dual citizens of Sweden and Britain. So far he has been proved right. Western ambassadors in Beijing dispatched a letter to the minister of public security in February expressing “growing concerns over the Chinese government’s commitment to the rule of law and basic human rights,” according to The Post’s Simon Denyer. The regime didn’t bother to reply.

It’s time for Mr. Xi’s abuses to rise to the top of the U.S.-Chinese bilateral agenda. President Obama should raise the case of Mr. Wen’s family with Mr. Xi when they meet — and point out that his heavy-handed repression is not only wrong, but also dangerous. Contemporary China will not tolerate a return to Maoism.