The biggest enemy of Park Geun-hye, the presidential candidate of the ruling Saenuri Party, is neither Ahn Cheol-soo, an entrepreneur-turned-professor who declared his independent candidacy for president on Wednesday, nor Moon Jae-in, the standard-bearer of the main opposition Democratic United Party.

Her worst enemies are within her own party. They are none other than her aides and people close to her. They are supposed to support her bid to become the nation’s first female president but are actually ruining it by getting involved in corruption scandals.

The latest case involved Song Young-sun, a former lawmaker who has long been a member of the pro-Park faction of the ruling party. She reportedly asked a local businessman for 150 million won, saying she needed the money to help Park win at least 60,000 votes in Namyangju, her electoral district in Gyeonggi Province, in the December election.

In return for the money, Song promised, according to a transcript released by a local daily, to help him acquire and develop land lots in a development-restricted green belt in Namyangju. Song further said she could be appointed as minister or vice minister of defense should Park win the election.

Embarrassed by the report, the ruling party expelled Song even before hearing any explanation from her or checking whether or not the report was true. The party’s knee-jerk reaction was understandable, given that the scandal broke out only one day after Hong Sa-duk, one of Park’s key aides, bolted from the party.

On Monday, the National Election Commission accused Hong, co-chairman of Park’s primary campaign team, of having accepted 60 million won ($53,600) in illegal political funds from a businessman between last autumn and March. Hong claimed innocence but left the party voluntarily to minimize the fallout.

In another case, former lawmaker Hyun Ki-hwan, a close aide to Park who was on the party’s candidate screening board in the April 11 general election, is under investigation. He was charged last month with receiving 300 million won from Rep. Hyun Young-hee in return for helping her win the party’s nomination for proportional representation.

These incidents are all the more embarrassing given Park’s pledge to root out political corruption. Dismayed by the indictment of President Lee Myung-bak’s aides on corruption charges, Park pledged to reform politics and to create a corruption-free political environment.

Yet the first order of the day for her is to ensure that people close to her do not get involved in corruptive practices. She needs to warn them sternly against riding on her coattails to pursue personal or illegal gains.

Following the report on allegations against Song, the ruling party set up a political corruption reporting center, saying that any tip-off would be immediately investigated by the party’s ethics committee.

The party needs to redouble efforts to prevent its members from committing corruption. This is necessary in light of Park’s slipping approval rating. A latest poll showed her rating fell below that of Moon Jae-in for the first time. She can’t afford any more scandals.