New Scandal Engulfs South Korean Leader in Wake of Marine’s Death

The South Korean marines were sent in after monsoon rains flooded a rural section of the country’s heartland last July. They were looking for missing residents in waist-high floodwaters, but they were not wearing life jackets. Nor did they have buoys or safety tubes.

When the ground gave way, five of them were swept away in the churning brown water and one, Lance Cpl. Chae Su-geun, disappeared downstream, yelling for help, and was later found dead.

Nearly a year later, the death of the 20-year-old marine has become an impeachment threat for South Korea’s leader, President Yoon Suk Yeol. And it has raised the prospect of political instability in the nation, a key United States ally in creating a bulwark against North Korea and China.

The South Korean military is no stranger to tragic accidents, but this latest episode has evolved into the first major political crisis for Mr. Yoon since his party’s crushing defeat in parliamentary elections last month. The career military officer who investigated Lance Corporal Chae’s death has accused the Defense Ministry of whitewashing the probe and absolving top military brass of responsibility — all under pressure from Mr. Yoon.

Mr. Yoon has not directly addressed the allegation, and last week the president vetoed a bill pushed through Parliament by the opposition calling for a special prosecutor to investigate the claim. The president wants government agencies like the police and prosecutors to finish investigating the various allegations before discussing other steps.

But there is wide public support for appointing a special prosecutor, surveys show, as many South Koreans have grown distrustful of Mr. Yoon and government prosecutors. Mr. Yoon’s opponents say that while prosecutors