THE STORY of Gui Minhai offers a measure of China's growing audacity in exercising "sharp power," or the use of sinister tools ranging from economic pressure and cyberattacks to illegal abductions, to silence its international critics. In October 2015, Mr. Gui, a Hong Kong book publisher and Swedish citizen, disappeared while on a visit to Thailand; it only gradually became clear that he had been secretly abducted by Chinese agents. Last Saturday, a few months after he was finally granted partial freedom, Mr. Gui was again kidnapped by security forces — this time on a train traveling to Beijing, and in full view of the Swedish diplomats who were escorting him.

In 2015, the regime of Xi Jinping might have worried that grabbing citizens of Western countries could produce a damaging backlash. Now it is content to do so openly, flagrantly violating international as well as Chinese law in full view of Western officials. That is probably because the response to its previous offenses has been, at best, muted.

Mr. Gui was one of five Hong Kong-based booksellers who were illegally arrested in 2015 by Beijing, which objected to their gossipy publications speculating about Communist leaders. The detentions were a flagrant violation of the autonomy guaranteed Hong Kong in the Sino-British agreement under which it was returned to Beijing's rule — not to mention the sovereignty of Thailand, where Mr. Gui was seized. But Britain, which was busy proclaiming a new "golden era " in relations with China, said little and did nothing, as did Thailand. Sweden mostly pursued silent diplomacy.

The latest incident provoked louder public protests from Stockholm, which said Mr. Gui was traveling with its diplomats to seek medical treatment at the Swedish Embassy in Beijing. He is said to have symptoms of amyotrophic lateral sclerosis, or ALS, a debilitating neurological disease, and was hoping to seek treatment abroad. If it is true, as Swedish officials have repeatedly been told, that Mr. Gui is at liberty after serving a sentence in China for a traffic violation, then there is no reason he should be denied Swedish consular services, much less be re-arrested.

China's foreign ministry could offer no coherent explanation for Mr. Gui's disappearance. Instead, at a regular news briefing, a spokeswoman said it was "not a matter that falls under the purview of the Ministry of Foreign Affairs," before going on to hint that it was Swedish Embassy officials who had somehow violated Chinese or international law. Perhaps the ministry was embarrassed by this preposterous performance; in any case, the statements about Mr. Gui were omitted from the official transcript.

By continuing to hold Mr. Gui, China's security services are once again deliberately risking the health of an internationally known political detainee; Nobel Peace Prize winner Liu Xiaobo died of liver cancer last July after being denied permission to seek treatment in the United States. You'd think Mr. Xi would wish to avoid another such embarrassment. But using sharp power evidently means never having to say you're sorry.

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