SEOUL — South Korea is facing an abrupt shift to liberal from conservative leadership with barely three weeks to go in an election campaign that underscores the deep split in a society that sees its ousted president on trial for trying to destroy his leftist foes.

A former provincial governor and city mayor, Lee Jae-myung, appears likely to take over the government after a “snap” presidential election on June 3 that could mark the end of a protracted crisis that began with the conservative who was president, Yoon Suk-yeol, declaring martial law on December 3.

The upshot was that Mr. Lee, whom Mr. Yoon had defeated by less than 1 percent of the vote in the previous election, in March 2022, not only got the national assembly to reject the martial law decree the same night but also rammed through the vote for impeaching Mr. Yoon. The constitutional court approved Mr. Yoon’s impeachment last month, leaving him to face trial in district court for “insurrection,” a crime that carries life imprisonment or the death penalty.

Mr. Lee, 61, was involved in real estate and construction scandals while mayor of Seongnam, just south of Seoul, and then, as governor of Gyeonggi Province, which surrounds the capital, faced charges of having bribed North Korea in a failed attempt to meet the North’s leader, Kim Jong-un. The court has postponed the latter case until after the election, making it unlikely he’ll ever go on trial.

Although a member of the left-leaning Minju, or Democratic Party, Mr. Lee is hardly a leftist. Lately he’s been praising leaders of the chaebol, the huge conglomerates that dominate Korean business, for their role in the economy’s success. He met the last American ambassador to Korea, Philip Goldberg, before Mr. Goldberg’s departure in January, and Minju leaders have seen the American charge d’affaires, Joseph Yun, filling in as ambassador.

Mr. Lee is appealing for broad popular support in the face of fervent conservative suspicion of the leftists who make up the hard core of Minju national assembly members. Many Minju members boast of having been jailed in their youth for joining in often violent protests against the dictators who ruled Korea before mass demonstrations ended dictatorial rule in 1987, giving rise to a constitutional democratic system guaranteeing popular elections for president.

At a rally Sunday night, Mr. Lee declared, “Our biggest goal is to restore democracy and peace in South Korea and revive the national economy” in the aftermath of the “insurrection” that he said still poses a threat from which he vowed to “save the country.”

Conservatives, though, appear just as determined to frustrate Mr. Lee, whom they often berate for what they say is his “criminal past.” In fact, for the past three years, this correspondent has heard many times that he is “going to jail” — something that has never happened. Conservatives also accuse him of making business deals with China, a country and society viewed with deepest suspicion for its support of North Korea and its dominant economic influence as the South’s leading trading partner.

Yet the conservative People Power Party faces one huge problem: It’s bitterly split over who should run for president. Just last weekend a former labor minister, Kim Moon-soo, 73, was reaffirmed as the PPP presidential candidate after the party tried to drop him in favor of a former prime minister, Han Duck-soo, who had served as acting president after Mr. Yoon’s impeachment.

A long-time senior bureaucrat who has served as economic minister and ambassador to Washington, Mr. Han quit as acting president and challenged Mr. Kim for the presidential nomination. With the PPP split into separate camps, Mr. Han has just endorsed Mr. Kim rather than face the blame for dividing the party, all but guaranteeing Mr. Lee’s victory.

Mr. Kim’s rise as a conservative leader would appear to have been extremely unlikely, considering that as a student he protested against dictatorial rule, was later jailed for demanding democratic elections, and served as governor of Gyeonggi Province before Mr. Lee. Although he did not support Mr. Yoon’s impeachment, he was not enthusiastic about his ill-fated attempt at imposing martial law.

Now Mr. Kim, as PPP candidate, is in the difficult position of having to apologize about Mr. Yoon, the man who named him labor minister. On local cable TV, Mr. Kim  said he wanted to “apologize  to the people who have suffered from the martial law imposition.” He acknowledged “the economy and domestic politics are in difficulty, and so are exports and diplomacy” — words that sound strangely similar to what Mr. Lee is saying.