How should the U.S. respond to China's Hong Kong power grab?

China’s legislature on Thursday approved a controversial national security law that gives the mainland government new powers to police subversion and foreign intervention in Hong Kong.

Critics of the new law say it’s a violation of the “one country, two systems” agreement that has granted Hong Kong certain levels of autonomy — like its own police force and judicial system — since the island became part of China in 1997 after more than a century of British rule.

The specifics of the law are unclear, but experts suggest it...