Negative campaigning is as universal as elections, and Korea is no exception. Almost every election -- big and small -- has been tainted by candidates who focus more on attacking rivals than promoting their own merits and policies.

This year, the impeachment of Park Geun-hye as president resulted in an unexpected early election, and with the May 9 election fast approaching, negative campaigning is raising its ugly head.

With major parties heading toward primaries to nominate candidates, no presidential hopeful is free from the problem of negative campaigning. The situation is most serious, however, in the liberal Democratic Party of Korea, which polls put as the most likely to win the upcoming election.

An opinion poll released Friday put the approval rating of frontrunner Moon Jae-in at 31 percent, and those of South Chungcheong Gov. An Hee-jung at 17 percent and Seongnam Mayor Lee Jae-myung at 8 percent. The fourth candidate, Ahn Cheol-soo of the People’s Party, earned 10 percent.

The three Democrats have a combined popularity of more than 60 percent, which means anyone who clinches the party’s ticket is highly favored to win the presidency. No wonder all three candidates are getting more anxious as Moon tries to maintain his lead and An and Lee endeavor to catch up.

Nevertheless, the mudslinging among the three -- especially between Moon and An -- is providing cause for concern.

In his latest attack on Moon, An accused the frontrunner of distorting his comments, saying Moon and his campaign team’s actions were “appalling and disenchanting.”

An went on to say that if the frontrunner maintained such an attitude, Moon would never be able to win power -- and even if he does, he will not be able to run the government successfully.

The basis for such an emotive tit-for-tat between the two had been created by their bitter confrontation over some issues, including An’s proposal to form a “grand coalition” that embraces the former conservative ruling party.

Moon accused An of seeking an alliance with a party that should bear the prime responsibility for the national crisis centered on the influence-peddling and corruption scandal involving Park and her confidante Choi Soon-sil.

Moon also criticized An for saying that Park probably had “good intentions” when she helped Choi with two foundations the president’s confidante allegedly used to take money from conglomerates.

There is no doubt that An’s grand coalition proposal and forbearance with Park are aimed at expanding his support base toward centrists and rightists who usually shun the liberal Democratic Party.

But An, who -- like Moon -- was a key aide to the late liberal President Roh Moo-hyun, runs the risk of alienating the liberal voters that he needs to rely on. His bitter attacks on Moon for inadvertently boasting about a military award he received from former President Chun Doo-hwan, who is still very unpopular among liberals, are one such case.

Whatever the motive, it is certain that -- as the campaign for the primary heats up -- the two candidates and their campaigners and supporters will engage in fiercer negative campaigning, which could leave a deep scar on the party.

The controversy over the leak of what is believed to be the result of an early vote for the party’s primaries is one good example that suggests the nomination race will deteriorate into a dogfight.

For now, the Democratic Party is highly favored to take power. Campaigns by its candidates should proceed in a way that befits the party’s standing. What they should not forget is that their standing is not the result of their own merits but the consequence of the public frustration with Park and her conservative party.