STARTING IN 2017, a picture slowly began to emerge from China’s far northwest: compounds surrounded by watchtowers, no trees, high fences, and reports of people being taken away without due process or explanation. Eyewitnesses and family members described how China was building a string of concentration camps for its Uighur minority and others, incarcerating more than 1 million Turkic Muslims in an attempt to eradicate their culture, language and identity, one of the most appalling human rights abuses in the world today.

China’s leaders first denied the camps existed, then later claimed they were schools for vocational education. But the evidence piled up that they were camps intended to wipe out the Uighur Muslim identity through mind-numbing lessons in Mandarin and demands that the prisoners renounce their religion, conform to the ways of the majority Han Chinese and respect the ruling Communist Party.

On June 29 last year, President Trump met in Osaka, Japan, with President Xi Jinping of China. According to former national security adviser John Bolton, in a new memoir, Mr. Trump used the meeting to beg Mr. Xi to buy American farm products to help with his reelection. Mr. Xi also defended China’s camps in Xinjiang. “According to our interpreter,” Bolton writes, “Trump said that Xi should go ahead with building the camps, which Trump thought was exactly the right thing to do.” Mr. Trump has called Bolton’s book a “compilation of lies and made up stories.”

In the meeting with Mr. Trump, the Chinese president probably did not call them concentration camps, and we do not know exactly how Mr. Trump replied. Presumably, there are interpreters’ notes in both countries. But if Mr. Trump provided so much as a wink or green light to Mr. Xi’s grotesque project in cultural annihilation, it marks another moral low in his presidency.

We already knew that Mr. Trump cared not a fig for human rights in China. He reportedly told Mr. Xi last year that he would soften the U.S. response to a crackdown in Hong Kong in order to get a trade agreement, his singular pursuit. But this willful disregard of repression has consequences. Mr. Trump’s message in Osaka was that he would not use the power of the presidency nor the influence of the United States to save the Uighurs from cultural extinction. He may have emboldened Mr. Xi to tighten the screws on Hong Kong this year. Mr. Trump sullies the values of human dignity and freedom that the United States has championed around the world for generations.

Within hours of leaks about Mr. Bolton’s book, Mr. Trump signed the Uighur Human Rights Policy Act, which includes possible sanctions against those involved in repression of the Uighur people. The law passed with overwhelming bipartisan support in Congress, a welcome sign that Mr. Trump’s contempt for human dignity is not the stance of the U.S. government nor of America itself. Mr. Trump was right to put his signature to it, whatever his motivation now. Standing up against coerced brainwashing, forced incarceration and destruction of a people’s heritage is “exactly the right thing to do.”

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