South Korea’s powerful political opposition has turned impeachment into its weapon of choice in its war against the conservative government.

The national assembly, dominated by the Minju or Democratic Party, has voted “unanimously” to impeach the acting president who was sitting in for the president, Yoon Suk-yeol, whom the assembly impeached just two weeks ago.

The vote deepened the discord of a governing system — and a society — that’s sharply divided between the left-leaning Minju and the conservative People Power Party of Mr. Yoon. He retains the title but not the power of president while the constitutional court decides whether to approve the motion to impeach him. 

The vote against the acting president, Han Duck-soo, was 192 to zero after all members of the supposedly “ruling” People Power Party boycotted the session. The assembly speaker said a simple majority of the 300 members sufficed to get rid of Mr. Han. As prime minister, he had automatically taken over as acting president after 204 assembly members, slightly more than the two-thirds required to impeach a president, voted against Mr. Yoon.

The impeachment of Mr. Han, a former ambassador to Washington much liked by the American foreign policy establishment, showed the drive of the Minju to force the constitutional court to approve Mr. Yoon’s impeachment. Mr. Han was graceful in bowing out of the acting presidency, saying he respected the assembly’s vote. 

The Minju staged the latest impeachment vote after Mr. Han balked at a Minju scheme for naming three judges to fill three vacant seats on the nine-member panel. The votes of six of the nine judges are needed to approve an impeachment motion.

Mr. Han “argued that appointing justices without bipartisan agreement would violate long-standing constitutional norms,” a Seoul website, NK News, said after the Minju rammed through a vote in the assembly for appointing three judges. The People Power Party “boycotted the vote,” NK News reported, “arguing that Han lacks the authority to make such appointments before the impeachment trial concludes.”

The Minju is also expected to attempt to impeach the new acting president, Choi Sang-mok, unless he bows to its will and signs legislation for filling out the court. As deputy prime minister for economic affairs, Mr. Choi is expected to prioritize confidence in Korea’s stock market and currency, whose value against the dollar has plummeted in recent weeks.

Mr. Choi said he’s hoping to bring about “national stability,” including strong defense against North Korea and tight relations with South Korea’s American ally. “South Korea’s foreign policy will remain unchanged,” Seoul’s Yonhap News quoted him as saying. “International exchanges and trade will not be disrupted.”

The Minju, led by the man whom Mr. Yoon narrowly defeated in the 2022 presidential election, Lee Jae-myung, is avoiding those topics while charging Mr. Yoon with “insurrection” for his brief attempt at imposing martial law on December 3.

The constitutional court has opened what’s likely to be a protracted process in which Mr. Yoon will argue that he acted legally not only in issuing a martial law decree but in withdrawing it six hours later after the assembly voted it down as troops surrounded the assembly.

The Minju, though, is expected to settle for nothing less than Mr. Yoon’s ouster — and a vote for a new president in a snap election. If the court rules against impeachment, mass protests by left- and right-wing factions would be sure to intensify.