Knife Attack on Opposition Leader Raises Alarms in Polarized South Korea

The man accused of stabbing Lee Jae-myung, the leader of South Korea’s main opposition party, in the neck had been stalking him in recent weeks, including attending a political event where Mr. Lee was present on Dec. 13, apparently captured on video there wearing a blue paper crown, the police say.

At a rally on Tuesday, a man wearing a similar paper crown and carrying a message supporting Mr. Lee and his party was also carrying something else: a knife with a five-inch blade and a plastic handle wrapped with duct tape.

The attack, the worst against a South Korean politician in nearly two decades, seriously wounded Mr. Lee, who officials said was recovering in an intensive care unit at Seoul National University on Wednesday after surgery. And it deeply shocked a country that values hard-won years of relative peace after an era of political and military violence before establishing democracy in the 1990s.