THE PRO-DEMOCRACY demonstrations that rocked Hong Kong last year have lulled, in part because the city is under partial lockdown to prevent the spread of the coronavirus. You’d think Chinese Communist authorities and their hugely unpopular representatives in the city would breathe a sigh of relief and focus on keeping the population healthy. Instead, they chose last week to escalate the repression of opposition leaders.

On Friday, police arrested Jimmy Lai, the founder of the pro-opposition newspaper Apple Daily, along with two well-known politicians, Lee Cheuk-yan and Yeung Sum. They were charged with participating in an unauthorized march more than six months ago, on Aug. 31, a day hundreds of thousands took to the streets, prompting bloody assaults by police. Mr. Lai was also charged with criminal intimidation for a 2017 incident in which he exchanged words with a pro-regime journalist.

Why now? It may be that Beijing sees an opportunity to dispose of key opponents in Hong Kong while the country and the world are preoccupied with the epidemic. A hard-line ally of President Xi Jinping was recently installed as head of the office overseeing the region. Days before the arrests, authorities announced that the head of a Hong Kong publishing house that produced uncensored books about Chinese leaders, Gui Minhai, had been sentenced to 10 years in prison.

Or maybe the regime was offended by the latest op-ed by Mr. Lai, a self-made millionaire who regularly assails Mr. Xi in the pages of the Wall Street Journal, among other publications. In a Feb. 19 op-ed, Mr. Lai bluntly declared that “the spread of the coronavirus has revealed a truth that poses a much greater risk to Mr. Xi: There is no cure for Chinese communism except the collapse of the party.” His point was that the suppression of information that helped the virus spread has only reinforced the corrosive distrust with which the regime is regarded by both the world and its own people.

Mr. Lai, who is in his early 70s, was released on bail but could face trial in the coming months. Hong Kong’s legal system, which was supposed to remain independent via the “one country, two systems” formula under which the former British colony was returned to Chinese sovereignty, no longer can be counted on to uphold the rule of law. A high-profile prosecution of the publisher of the city’s most outspoken newspaper would underline that shift for the foreign investors on whom Hong Kong’s prosperity depends. But as the recent history of tumult in the city has repeatedly shown, Mr. Xi is nothing if not shortsighted.

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