CHINA’S CRACKDOWN on lawyers and human rights defenders is not a single event but a rolling onslaught. Last month, three prominent rights activists were detained by police in separate provinces. What makes these detentions so pernicious is that China’s security apparatus has targeted the backbone of the rights movement: lawyers and defenders who represent the accused. The latest detentions are part of President Xi Jinping’s broader campaign to snuff out opposition to the ruling party-state wherever it can be found.

Liu Feiyue, one of the activists recently arrested, started a website in 2006, Civil Rights & Livelihood Watch, or Minsheng Guancha. The website has documented protests, land seizures, detentions and other human rights violations that often go unreported by the official Chinese news media. Mr. Liu’s website, one of the few located on the mainland to courageously expose such stories, was blocked in China soon after it was launched. He was undeterred.

For two decades, Mr. Liu has been repeatedly detained, harassed and put under surveillance by the authorities. He was routinely taken in during politically sensitive events such as sessions of the Chinese party congress and legislature. But this time, the charges appear to be more serious. He was detained in mid-November in the central Chinese province of Hubei and police informed his relatives the charges were “incitement to subvert state power,” which carries a maximum sentence of life in prison and is frequently used to silence journalists and dissidents. An unnamed volunteer in his group told Radio Free Asia that Mr. Liu is being prosecuted for accepting overseas funding to run his activities, but did not provide details. The overall crackdown has included new laws that impose sharp restrictions on foreign nongovernmental organizations that work in China.

Also detained recently was prominent lawyer Jiang Tianyong, a leader of the China Human Rights Lawyers Group, who disappeared Nov. 21 when he had been due to board a train from the city of Changsha in Hunan province to Beijing. He had been in Changsha attempting to visit the wife of a fellow attorney who was among those taken in a wave of arrests of lawyers that began in July 2015. Mr. Jiang’s clients have included the blind lawyer-activist Chen Guangcheng, now living in the United States.

Yet another rights activist, Huang Qi, the Sichuan-based founder and director of a human rights group called 64 Tianwang, was taken from his home Nov. 28 by police. He, too, has been detained and imprisoned several times for his work and his website is blocked inside China. A volunteer, Pu Fei, initially published news of his detention on Twitter, but that message was deleted and Mr. Pu has also disappeared.

Every effort must be made to speak up for those who are hustled away in the middle of the night. President-elect Donald Trump has shown little interest in human rights, but after he takes office he should not remain silent about these cases, because silence only encourages more repression.