Members of South Korea’s oppositionscatter365, which controls the National Assembly, have submitted a motion to impeach President Yoon Suk Yeol after his ill-fated decision to impose martial law.

If Mr. Yoon quits or is removed from office then, under the constitution, Prime Minister Han Duck-soo will step in to perform presidential duties.

Mr. Yoon, a conservative, came into office after winning the 2022 presidential election by a threadbare margin, and appointed Mr. Han as the prime minister that year. It marked Mr. Han’s second time in that job; he had served under President Roh Moo-hyun, a liberal, from April 2007 to February 2008.

Mr. Han began his career as a civil servant in the early 1970s, working on trade and industrial policy for decades. He received a doctorate in economics from Harvard in 1984. From 2009 to 2012, Mr. Han was South Korea’s ambassador to the United States.

Mr. Yoon has been in a bitter standoff with the opposition, led by the progressive Democratic Party, for almost his entire tenure as president. The Democratic Party inflicted a crushing defeat on his People Power Party in the parliamentary elections held in April, leaving him on the verge of being a lame duck.

The Democratic Party has said it would begin impeachment proceedings if Mr. Yoon does not step down immediately. The president is impeached if two-thirds of the 300-member legislature vote in favor of doing so.

Mr. Han would act as the president until impeachment proceedings conclude. How long he would need to serve in that interim capacity is unclear.

Under South Korean law, once the National Assembly has impeached the president, the matter could go to the Constitutional Court. If the court upholds the impeachment, the president would be removed from office.

If Mr. Yoon is removed or steps downscatter365, a successor would need to be elected within 60 days.

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