South Korea’s conservative former top prosecutor, who has called for a stronger U.S. security guarantee to neutralize North Korean nuclear threats, won the main opposition party’s hotly contested nomination for next March’s presidential election on Friday.

Recent opinion surveys showed Yoon Suk Yeol would be locked in a tight race with Lee Jae-myung, the outspoken liberal ruling party candidate, who has vowed to take an appeasement policy on North Korea and adopt pragmatic diplomacy between Washington and Beijing.

The close race between the two candidates will likely further intensify severe domestic polarization in South Korea at a time when it faces growing North Korean nuclear threats, an intense U.S.-China rivalry and various economic woes. 

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A victory for Yoon could lead to South Korea taking steps to bolster its military alliance with the United States while its ties with North Korea and China may sour. If elected, Lee would push for greater ties with North Korea but he may not be able to convince the country to abandon its nuclear program, possibly sharing the legacy of his party colleague and dovish current President Moon Jae-in, whose single five-year term ends in May.

In the opposition People Power Party’s convention on Friday, party authorities announced that Yoon garnered 47.8% of the votes cast by party members and general citizens, beating his main rival Hong Joon-pyo with 41.5% and two other competitors. 

“The government must be very frightened and feeling bitter pains about my victory at the party primary,” Yoon said in an acceptance speech. “I’ll surely achieve a shift in power … I’ll surely rebuild a new Republic of Korea.”

Yoon, 60, has spent most of his professional career as a prosecutor but is a novice in party politics.

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He was also previously Moon’s prosecutor general, who led the president’s contentious anti-corruption campaign that largely focused on conservatives including those aligned with the People Power Party. But Yoon was later embroiled in high-profile political strife with Moon’s allies after some of his investigations targeted Moon associates.

Moon’s supporters argued Yoon’s investigations were politically motivated to elevate his own political standing or disrupt Moon’s push to reform the prosecution. Yoon denied such views, saying his investigations followed due, fair procedures. 

The infighting triggered a domestic political firestorm, undermined Moon’s anti-corruption drive and boosted Yoon’s popularity. He eventually resigned the top prosecutor’s post in March and joined the People Power Party in July.

Yoon has since pledged to strive to end liberal rule, accusing the Moon government of “trampling on fairness and justice” while being “corrupt” and “anachronistic.” 

Yoon’s opponents have attacked him over a lack of expertise on security and other major issues. Yoon said Friday he would select competent experts regardless of their political lines and let them handle key affairs. 

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“Yoon himself does not have a foreign policy record, but he has a deep pool of experienced advisers. The question is whether he will listen to and adjudicate different opinions among them,” said Leif-Eric Easley, a professor at Ewha University in Seoul.

In his Friday speech, Yoon said he would push for North Korea’s denuclearization more effectively though coordination with the international community, but didn’t elaborate. 

But in September, Yoon said if elected he would talk with Washington to formulate procedures on the deployment of U.S. nuclear weapons in case of emergency and conduct related joint training to boost the reliability of the U.S. “nuclear umbrella” security commitment offered to allies. 

But he later suggested he would oppose the U.S. reinstalling tactical nuclear weapons in South Korea, which it withdrew in the 1990s, because that would deprive Seoul of its legitimacy in calling for North Korean denuclearization. He said it would be “more realistic” to ask Washington to send submarines carrying nuclear missiles around the Korean Peninsula as deterrence against potential aggression from North Korea. 

Yoon has also said he would prepare for economic cooperation with North Korea but link it to progress in Pyongyang’s steps toward denuclearization, a policy that North Korea won’t welcome.

How to deal with North Korea has long sharply split South Koreans. Conservatives have called for tougher sanctions and pressures in close coordination with the United States to get North Korea to give up its nuclear ambitions. But liberals favor a negotiated resolution of the nuclear issue while often prioritizing improved ties with North Korea over South Korea’s U.S. alliance.

Moon’s government once brokered high-profile nuclear diplomacy between Washington and Pyongyang, but their talks collapsed in early 2019 because they differed over how much sanctions relief the United States should provide to North Korea in return for dismantling its main nuclear complex, a limited disarmament measure.