For President Xi Jinping of China, Deng Xiaoping’s advice on how China should rise — “keeping a low profile” — was yesterday’s story. Discretion is not his thing.

Since Xi became president in 2013, he has made China’s ambitions abundantly clear, upping the ante on the strategic, military, technological and economic fronts. The United States is now in a direct ideological war with China over the shape of the world in the 21st century.

The trade war between the United States and China, and the brave protesters in Hong Kong fighting for the preservation of the rule of law against the threat of absorption into lawless Chinese authoritarianism, are facets of this overarching confrontation. If you focus on the signal and not the wildly gyrating noise, President Trump has gotten China policy about right. Even a stopped clock is right twice a day. It was time to draw a line in the sand against Xi and his overreach.

A victim of Mao’s ruthlessness during the Cultural Revolution, Xi absorbed the lesson that ruthlessness is the sine qua non of authoritarian one-party rule. He has abolished the very term limits designed by Deng to prevent the emergence of another Mao-like figure, installing himself as quasi-emperor for life.