South Korea's main opposition party introduced a bill to impeach acting President Han Duck-soo on Thursday, a day before it plans to seek a vote on the move, which could deepen a constitutional crisis triggered by a short-lived martial law.

President Yoon Suk Yeol vowed to “fight to the end,” despite the opposition’s push to impeach him and his own party’s demand that he resign.

For the United States, the turmoil in South Korea is potentially disruptive to its geopolitical agenda in East Asia.