The political purge of Tran Duc Anh Son, an expert on Vietnam’s claims in the South China Sea, is a rare window into how the party handles dissent among its rank-and-file members.

On April 17, Mr. Nishimura Yasutoshi, Minister of Economy, Trade and Industry, held a meeting with Mr. Tran Tuan Anh, Head of the Central Economic Committee of the Communist Party of Viet Nam. Both ...