“JUST IN CASE I AM IMPRISONED,” Pham Doan Trang wrote across the top of a letter she gave to a fellow dissident for safekeeping last year. Vietnam’s most prominent democracy activist anticipated her arrest, which came Tuesday, when she was accused of “making, storing, distributing or disseminating information, documents and items against the Socialist Republic of Vietnam.” Her letter was made public, and it contained a remarkable appeal.

“No one wants to sit in prison,” she said. “But if prison is inevitable for freedom fighters, if prison can serve a pre-determined purpose, then we should happily accept it.”

“I don’t want freedom for just myself; that’s too easy,” she wrote. “I want something greater: freedom for Vietnam.”

She urged people not to campaign for her release, but instead to seek democratic reforms, including free and fair elections for the National Assembly, and to focus on her writings and books about political rights, with titles such as “Politics for the Common People,” “Politics of a Police State,” “Citizen Journalism,” “A Handbook for Families of Prisoners” and others. If interrogated by the authorities, she vowed that she “will not admit guilt, confess, or beg for leniency,” but “will always assert that I want to abolish dictatorship in Vietnam.”

She also wrote: “Please take care of my mother.”

Ms. Trang’s arrest is the latest and one of the most flagrant in Vietnam’s long practice of squelching freedom of expression and political dissent, including arrests of bloggers and independent journalists. The repression appears to be intensifying ahead of a Congress of the Communist Party of Vietnam, held every five years, expected in January. Ms. Trang is being held incommunicado, a common practice in such cases. Article 117 of the Vietnamese penal code, under which Ms. Trang and others have been charged, carries a potential 20-year prison term. She told Radio Free Asia in May, “Freedom has always been restricted, but nowadays it seems to be narrower, and there’s more and more violence. From now until the party congress, the scope of freedom can be tightened more and more, and the suppression will increase.”

Her arrest came just hours after the United States and Vietnam had finished the 24th Annual U.S.-Vietnam Human Rights Dialogue, a three-hour virtual meeting that the State Department said “addressed a wide range of human rights issues.” That Vietnam would seize its best-known democracy activist on the heels of the meeting says much about the diminished standing of the United States in the world under President Trump, who has repeatedly ignored human rights abuses while cozying up to the world’s despots.