SEVERAL DAYS ago we suggested that U.S. adversaries such as China could exploit the chaos in Washington created by President Trump’s refusal to accept his election loss. As it turned out, Beijing didn’t wait long. On Wednesday, it orchestrated the transformation of Hong Kong’s semi-democratic legislature into a rubber-stamp body like those that grovel before the regime in Beijing. It was the most blatant violation yet of China’s promise to preserve Hong Kong’s political autonomy and rule of law until 2047 — and yet another blow to the global cause of democracy on the Trump administration’s watch.

Hong Kong’s legislature, created by Britain in 1985, has never been fully democratic, but opposition legislators managed to gain a substantial minority of seats in recent elections, allowing them to slow or block legislation. Under pressure from Beijing, Hong Kong’s government has been trying to contain the pro-democracy bloc by disqualifying some candidates, bringing criminal charges against others and postponing elections scheduled for this fall that looked likely to produce an anti-regime landslide.

On Wednesday, the repression sharply escalated. In Beijing, the Communist-dominated National People’s Congress Standing Committee adopted a measure banning Hong Kong legislators who “publicize or support independence,” “seek foreign interference,” or pursue “other activities that endanger national security.” It was the second time in five months that Beijing had directly intervened in Hong Kong’s affairs, violating the commitment it made when Britain returned Hong Kong to Chinese sovereignty in 1997.

Shortly afterward, the Hong Kong government stripped four legislators of their seats. One, Alvin Yeung, was disqualified for having signed a letter calling on the U.S. Congress to pass a bill mandating sanctions on Chinese officials who sponsored repression in the city — a bill co-sponsored by Sen. Kamala D. Harris (D-Calif.), who is now the vice president-elect. Fifteen other pro-democracy legislators responded by quitting the legislature, leaving its pro-Beijing faction with a 39-to-2 majority.

Some in Hong Kong questioned whether the resignations were self-defeating; the government will now be able to more easily pass repressive laws. Yet the People’s Congress action made clear that the regime of Xi Jinping intends to allow no more political dissent in Hong Kong than on the mainland — which is to say, none.

It’s probable Beijing would have shut down the opposition legislators at some point even without turmoil in Washington. But the spectacle of Mr. Trump sulking in the White House while purging the Pentagon of competent personnel can only be an inviting prospect; China may not be done taking advantage. Effective response to the Xi regime will have to await the inauguration in two months of President-elect Joe Biden, who has rightly pledged to work with U.S. democratic allies as China intensifies internal repression and external aggression. For now, Mr. Trump has handed Mr. Xi, Vladimir Putin and other U.S. adversaries an open field.

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