CHINA’S FRANTIC campaign to crush the so-far nonexistent “jasmine revolution” has now swept up one of the country’s best-known artists. Ai Weiwei, a sculptor, filmmaker, architect and performance artist who helped design the “Bird’s Nest” stadium at the Beijing Olympics, was detained in the Beijing airport Sunday and had not been seen or heard from more than 24 hours later. Mr. Ai had been pushing the boundaries of free expression in China. On his Twitter account, which has more than 70,000 followers, he was keeping track of the lawyers and dissident intellectuals who have been arrested in a far-reaching crackdown during the past two months. Now he is one of them.

According to a count by the Chinese Human Rights Defenders group, 26 political suspects have been arrested in China since February, and the government has restricted the movements of 200 more. Another 30 have, like Mr. Ai, simply disappeared. They include a China-born Australian spy novelist and six lawyers from Beijing, Guangzhou and Shanghai who often take on human rights cases. Some of those who have surfaced in the legal system have been charged with “inciting subversion of state power,” the same offense for which Liu Xiaobo, the winner of the 2010 Nobel Peace Prize, is serving an 11-year prison term.

In addition to the arrests, police have been swarming downtown locations in Chinese cities on Sunday afternoons, and new restrictions have been imposed on foreign journalists. All of this has been prompted by the thinnest of threats: calls on Web sites outside of China for “jasmine” protests, including “strolls” through city centers. There have been no protests, but the regime’s security forces have reacted as if the eruption of a Chinese version of the Tunisian or Egyptian uprisings is imminent.

One of Mr. Ai’s apparent offenses was to puckishly feed that paranoia. “Today we are all Egyptian,” he tweeted back in February, according to the Los Angeles Times. “It only took 18 days for the collapse of a military regime which was in power for 30 years and looked harmonious and stable. This thing [the Chinese government] that has been for 60 years may take several months.”

In fact, there is no sign that China will experience a popular uprising soon. In contrast to the Middle East, living standards and economic opportunity are expanding for its young generation. Still, the regime’s fearful reaction is suggestive; so are the statements from some of its most senior leaders that the rising prosperity will be curtailed without political reforms. At least some of China’s leaders appear to understand that the authoritarian status quo is untenable; they also seem to know what a refusal to change can lead to. But they don’t appear able, for now, to do anything about it — other than the pointless and counterproductive persecution of people such as Ai Weiwei.