Lee Jae-myung was set to become the presidential candidate for South Korea's ruling party on Sunday, hoping to overcome a property scandal and gather national support while conservative opponents trade barbs over anal acupuncture and fortune tellers.
Lee, the governor of Gyeonggi province, was expected to seal his victory in the primary to represent the Democratic Party primary in the March 9 presidential election.
The leading contender to among a fractured field from the main conservative People Power Party, Yoon Seok-youl, has been caught up in scandals of his own - including murky ties to an anal acupuncturist and accusations he relies on fortune-tellers.
"It used to be at most a single candidate who had such scandals, but the top two frontrunners are both embroiled in scandals in this election, which shows South Korea is regressing politically," said Lee Jun-han, professor of political science at Incheon National University.
The winners will vie to replace President Moon Jae-in, who must step down due to term limits.
Lee leads more than 55% of the vote to his nearest rival's 34% in the primary ending on Sunday, which began early last month. Results are expected around 6 pm.
Dogged by a scandal involving a residential development plan when he was mayor of Seongnam in 2015, Lee is seeking to focus to his agenda, including a push for universal basic income and more affordable housing amid skyrocketing property prices.
Prosecutors and police have been investigating the Seongnam project amid controversy over Lee's ties to a former official, who has been arrested on corruption charges related to the deal.
Lee has denied any wrongdoing. His office did not respond to requests for comment.
Housing-related scandals are a particular sore spot for voters in South Korea, where home prices have soared beyond the reach of many. Lee's party has been damaged by allegations of property speculation.
On the other side, conservative Yoon - a former top prosecutor who joined the opposition after gaining prominence during a political fight with President Moon - was forced in a televised debate last week to distance himself from an unlicensed anal acupuncturist.
Yoon denied knowing the acupuncturist, and said he only "seldom" meets fortune tellers or shamans.
Yonhap news agency said prosecutors are investigating a political meddling scandal that possibly involves Yoon. It quoted him as calling the allegations a "political plot" to derail his candidacy.
Yoon has denied any wrongdoing while serving as a prosecutor. His campaign did not respond to Reuters requests for comment.
His rival in the PPP primary, Hong Joon-pyo, on Saturday called a possible matchup between Lee and Yoon a "criminal election" where two outlaws will compete against each other.
The conservatives made gains in local elections in April as the Democratic Party was mired in scandals, but the primary spats over things like shamanism threaten their chances to capitalise in the regular election, said Yang Seung-ham, a longtime political analyst.