Even against the drama of modern Korea, which is taking so many twists and turns these days, the arrest of South Korea’s impeached president, Yoon Suk-yeol, is shocking.

Having holed up behind his security service in the presidential mansion since his abortive attempt at imposing martial law on December 3, Mr. Yoon now faces not only grueling interrogation but also a possible show trial that could result in the same fate as that of two other conservative presidents — a lengthy prison term.

The fact that it was Mr. Yoon who freed those two — the daughter of the long-ruling strongman Park Chung-hee, Park Geun-hye, and the one-time Hyundai top executive, Lee Myung-bak — adds to the bitter irony. That’s if the constitutional court upholds the impeachment of Mr. Yoon by the national assembly and he’s stripped of the title of president. 

Mr. Yoon retains that title, even though he’s lost the authority of the job and is in jail awaiting possible trial for “insurrection” by declaring martial law. Yet the downfall of a president who had endeared himself to American officialdom by endorsing joint American-South Korean military exercises is extraordinary — as is so much else here since the invasion of the South by North Korean troops in June 1950 and the entry of Chinese forces late that year.

Memories of the Korean War, overtaken by the Battle of Vietnam, may have faded. North Korea’s success, though, in developing nuclear warheads and the missiles to send them to distant targets reminds us that “the forgotten war” that ended in an armistice, but not a peace treaty, is not over. 

The leadership struggle in the South between rightists and leftists  provides a counterpoint to the draconian rule of North Korean leader Kim Jong-un — even though Americans may wonder why they should care. Standing up to Communist Chinese expansionism in the Indo-Pacific ranks as one major reason. 

“The United States has supported South Korean security, but in turn the South has supported the United States,” a long-time researcher for the Rand Corporation, Bruce Bennett, tells the Sun. “If one is looking for places to base U.S. air forces on the periphery of China, South Korea is a really good option. And the same would be true for the theater missiles that the U.S. services are developing.” 

As if to underline the immediacy of the Korean crisis, North Korea this week test-fired short-range missiles after having tested a long-range hypersonic missile ten days ago. Talking to the Sun, a former deputy secretary of state in the first Trump presidency, Stephen Biegun, cited the dangers of nuclear proliferation throughout Northeast Asia, including Communist China as well as North Korea.

A one-time point man on North Korea, Mr. Biegun warned that South Korea, followed by Taiwan, might go nuclear if Americans lost interest in Korean issues. Mr. Trump, he hinted, might try again to see Mr. Kim as he did three times during his presidency.

The turmoil in South Korea, though, raises the question, so what if all these caterwauling politicians are battling one another? In the more than seven decades since the Korean War, Korea has seen coups, dictatorial rule, arrests and trials of former presidents despite adoption, in 1987 after mass protests,  of a “democracy constitution”guaranteeing regular elections.

Chaos in Korea could get much worse as Mr. Yoon’s adherents gain in numbers. “A seemingly exhausted public is looking for relief,” writes a long-time analyst of Korean affairs, Shim Jae Hoon. He cites a Korea Gallup poll  showing  Mr. Yoon’s approval rate “making a comeback, from a wretched 14.8 percent before the impeachment, to 36.9 percent in the first two weeks of January, a spectacular gain of 22.1 percent.”

Voters are “looking for stability,” says Mr. Shim.

Passions on both sides are boiling. An ardent foe of the Minju tells the Sun “they are all dogs and should be wiped out.” Mr. Shim quotes a hot-headed  radical Minju assembly member calling for “a death sentence” on Mr. Yoon.