President Moon Jae-in and his aides have kept mum about Wednesday’s decision by the Supreme Court to uphold the conviction of South Gyeongsang Province Gov. Kim Kyoung-soo for his involvement in an online opinion-rigging scheme ahead of the 2017 presidential election.

Their silence appears to reflect their perplexity about the top court’s ruling that could cast doubts on the legitimacy of Moon’s victory in the election. Kim played a key role in Moon’s campaign team.

Kim was elected to the gubernatorial post in 2018, of which he was stripped following the confirmation of his conviction. He will be put behind bars again within days. He was released on bail in April 2019 after serving 77 days following the first court ruling.

Under the relevant law, Kim is banned from running for public office for five years after he is set free in 2023.

In January 2019, the Seoul Central District Court sentenced him to two years in prison for colluding with a group of online bloggers, including Kim Dong-won, known by his alias Druking, to illegally generate opinions in favor of Moon ahead of the last presidential vote. It also added another 10 months in jail with a stay of execution for two years to the sentence for Kim’s violation of the election law. He was accused of offering the post of consul general in Sendai, Japan, to an associate of Druking in return for the secret cyber operation.

In November, the appeals court also concluded that he knowingly participated in the opinion rigging scheme, but found him not guilty of violating the election law.

The Supreme Court dismissed Kim’s claims that he was not aware of Druking’s use of computer software to rig public opinions online. It upheld the ruling by the appellate court to acquit him of violating the election law but did not rule out the possibility that the diplomatic job was offered in return for the secret online operation.

Despite the top court’s judgment, Kim still maintained his innocence, saying he would not abandon the belief that “truth will eventually be back to its place how far it is thrown away.”

His remarks sounded hollow to most people, who see him as just trying to disguise and distort the truth.

Rather, there are rising calls for more light to be shed on all other matters related to the opinion rigging scheme.

The focal point of attention is whether Moon knew of the scheme designed to benefit him in the presidential race. Given Kim is a close associate of Moon -- he managed Moon’s campaign schedule -- it seems reasonable to suspect that he was aware of the opinion rigging operation.

Officials at Cheong Wa Dae have said the presidential office has no specific position on the top court’s conviction of the governor, declining to comment on Moon’s response to the ruling.

It makes no sense for the presidential office not to declare a position on a grave issue that could undermine the legitimacy of Moon’s election win.

At the moment, it may go too far to assert Moon’s legitimacy as president has been put into doubt. But Moon should at least come forward to apologize for the opinion rigging case, as demanded by his rival candidates in the previous presidential election and the main opposition People Power Party.

The ruling Democratic Party of Korea, which has tried to shield the governor from accusations against him, should now be in sync with the court judgment and voter sentiment.

The verdict should also serve as a warning to those involved in electioneering that they should not resort to illegal means.

With the next presidential vote set for March, there is the possibility that similar opinion rigging operations may be underway as competition is intensifying among presidential hopefuls.

Attempts to manipulate public opinion pose a severe threat to ensuring fair elections, which is a key pillar of free democracy.

It is necessary for the rival parties to agree on establishing a bipartisan mechanism to prevent a repetition of online opinion-rigging.