The central figure in the plot against the wife of President Yoon of South Korea testified Monday he photographed the first lady accepting a pale blue “Lady Dior pouch” to show she was exploiting her role for personal enrichment.

A Korean-American pastor, Choi Jae-young, talking to the press before entering Seoul Central District Court, portrayed himself as both crusading journalist and God-fearing Christian in response to the prosecutor’s claims that he had ensnared Mr. Yoon’s wife, Kim Koon-hee, in an attempt at bribery.

Acceptance of a Dior bag may not rate as a terrific offense by most international standards — certainly nothing to compare with the trials and traumas of American politicos — yet in South Korea’s tempestuous political climate, the whole show is more than an embarrassment to the conservative Mr. Yoon, who has offered “a deep apology to the South Korean people for causing concern due to my wife’s unwise conduct.”

Those words won’t mollify Mr. Yoon’s liberal/leftist foes, who increased their control of the national assembly by a wide margin in elections last month. At the center of what is known as Dior-gate, aside from the pastor, is the anti-Yoon publication Voice of Seoul, which has admitted one of its reporters bought the telltale bag to give to the president’s wife — plus the wristwatch with camera.

Now prosecutors are demanding not only the video shot by the pastor but also his copies of message traffic with her, according to the English-language Korea Herald. The pastor has acknowledged he got to meet her through a family connection with her father.

That kind of scenario is familiar to Koreans, long accustomed to relatives and workmates and friends of friends cozying up to politicians. “They’re all thieves,” an office employee,  Kim Sung-eun, told the Sun. “No one is honest. The pastor played an evil trick. He’s to blame, not her.”

Mr. Yoon’s allies are charging that the opposition Minjoo, or Democratic Party, racked up its huge majority in last month’s assembly elections by vote buying and counting — similar to claims that President Trump and his advocates make about the 2020 presidential election.

Mr. Choi said he deliberately filmed the president’s wife accepting a gift that far exceeded the legal maximum of one million Korean won, $731, to show her “true character,” according to JoongAng Ilbo, a leading Korean newspaper.

Prosecutors say Mr. Choi and Voice of Seoul conspired to trap her while she was doing her job as first lady. In the storm of publicity, prosecutors are not talking about bringing charges against her.

Mr. Choi talked to reporters on his way into the courtroom. JoongAng Ilbo quoted him as saying he was engaging in “undercover reporting.” He merely “intended to support the people’s right to know” — surely “not a crime.”

In an environment in which all sides exchange charges of corruption, influence-peddling, and even murder, the case of the president and the first lady stands for much greater offenses. The president’s wife has been accused of plagiarism and inflating details of her background, and his wife’s mother has been jailed for forgery in a stock scandal.

The leader of the opposition, Lee Jae-myung, whom Mr. Yoon narrowly defeated in the presidential election in 2022, also is under investigation for shady real estate dealings involving millions of dollars. Five people said to have known details of the case have committed suicide. Mr. Lee is still expected to run for president again in 2027.