FIVE YEARS ago, lawyer Nguyen Van Dai became co-founder of a pro-democracygroup in Vietnam called Brotherhood for Democracy, which was intended to underscore a fresh approach to activism. Instead of being lone campaigners for democratic principles, its members would attempt to unite the forces of dissent into a larger force, a “collective strength” based on “solidarity.”

On April 5, Mr. Dai’s hopes were dealt a severe setback. A court in Hanoi sentencedhim and five other activists to between seven and 15 years in prison for alleged subversion. Vietnam is ruled by a Communist Party that is intolerant of dissentand in recent months has been intensifying a crackdown on those advocating human rights and pushing for democracy. Mr. Dai, who served an earlier four-year prison term, was sentenced to 15 years. The brotherhood has said it is dedicatedto “fight to protect human rights recognized by the Vietnamese Constitution and international conventions” and to “promote the building of a democratic, progressive, civilized and just society for Vietnam.” Their lawyer, Le Luan, said, “At the trial today, no evidence showing the defendants’ attempt at overthrowing the state was given. The charge was very much groundless.”

Days later, another court in Thai Binh in northern Vietnamsentenced a member of the group,Nguyen Van Tuc, to 13 years in prison on the same charges. The official Vietnam News Agency said Mr. Tuc joined the group in 2014 and served as its vice president. It called the brotherhooda “reactionary organization that operated illegally aimed at attempting to abolish the leading role of the Communist Party of Vietnam and overthrow the people’s administration.” Mr. Tuc was previously sentenced in 2009 to four years in prison.

Vietnam remains locked in the Stalinist past when it comes to denying rights to its people, including bloggers and online commentators. In 2016, the authorities arrested a popular blogger, Nguyen Ngoc Nhu Quynh, who wrote under the pen name Mother Mushroom and was co-founder of a network of independent bloggers. At the time, she had been writing extensively about a chemical spill that devastated marine life and left fishermen and tourism industry workers jobless in four provinces. When taken into custody, Ms. Quynh was accused of publishing “propaganda” against the state. She is still in jail, and her health is deteriorating. Recently, Amnesty International saidit has counted 97 prisoners of conscience in Vietnam, including lawyers, bloggers, human rights defenders, environmental activists and pro-democracy campaigners.

Vietnam’s party bosses might have been somewhat less enthusiastic about snuffing out dissent if the United States were still party to the Trans-Pacific Partnership, the Asian trade agreement including Vietnam that President Trump abandoned last year. When in Hanoi last year, Mr. Trump didn’t even publicly raise concerns about a crackdown on dissidents. The Vietnamese leaders seem to feel unconstrained by worry about pressure from the United States. Their people are the biggest losers.