Sunday is the day Hong Kong fought over in 2014, when student-led demonstrators massed on downtown streets for 75 days. Angered by the erosion of Hong Kong’s rule of law, media freedom and other liberal institutions, they demanded that China’s central government honor its promise to let the semiautonomous former British colony elect its leader democratically. Beijing refused, so on Sunday a new Chief Executive will be imposed on the city in a precooked exercise sure to inflame local politics.

Despite the televised debates,...