How will the spy agency's alleged attempt to fabricate evidence in an espionage case affect the June 4 local elections?
There is a general consensus amongst experts that the "spy scandal" might work favorably for the opposition bloc, but they disagree on the extent of the impact on the overall results.
Kookmin University professor Mok Jin-hyu claimed that it will have no significance for the elections since it is basically not a political matter.
"The National Intelligence Service (NIS) is now cooperating in the prosecution's investigation, which is still ongoing," said Mok during a KBS radio interview. "I think it's not an issue significantly political enough to substantially affect the local elections."
However, Kim Yun-chul, head of Korea Society Opinion Institute, said the scandal will have an enormous impact on the polls given that the effects of any fallout from the probe will be felt by both President Park Geun-hye and the governing Saenuri Party.
Kim said that should Cheong Wa Dae fail to resolve the issue decisively, then the ruling party would ultimately pay a high price for the scandal.
"The alleged documentary forgery by the spy agency, if proved true, is a really serious matter. If it's not resolved soon by President Park or Cheong Wa Dae, it will have an impact on the elections."
Choi Chang-ryul, a political scientist at Yong In University, said, "Chances are high that the scandal is going to be a huge issue and sway voters in the polls. How far it will do so depends on how the opposition handles it."
Choi pointed out that if the opposition sticks to its call for appointing a special prosecutor, as it did repeatedly for some time over the NIS's alleged intervention in the 2012 presidential election, it might fail to attract voters.
The NIS is suspected of providing fabricated Chinese government documents for prosecutors to use in an appeals hearing in an espionage case against Yu Woo-sung, a former Seoul government official. Yu was indicted last year for allegedly passing on the personal information of some 200 defectors to Pyongyang, but found not guilty by a district court.
A special prosecution team began an official investigation last week into the alleged evidence forgery, but a suicide attempt by a key witness surnamed Kim, allegedly a North Korean defector with Chinese citizenship, added fuel to the controversy.
Kim is suspected of providing the agency with the forged documents detailing Yu's travel records to North Korea, and being paid for this by the NIS.
Some members of the ruling Saenuri Party are already showing signs of nervousness about how the scandal might affect their electoral fortunes in the upcoming polls.
And President Park Geun-hye's unprecedented expression of regret over the scandal Monday is indicative of the anxiety within the governing side.
Park said the controversy triggered by the alleged document fabrication was regrettable, and called for a thorough investigation.
The party leadership has taken a somewhat defensive stance, attempting to stress that the fabrication might just be the work of a few rogue NIS officers, rather than a coordinated operation.
However, some party members are complaining about what they call a lukewarm response.
Rep. Kim Yong-tae argued: "Party leaders need to pay more attention to public opinion as we approach the elections. I am worried about whether or not the people will choose us in June."
The second-term lawmaker joined the opposition's call for NIS Director Nam Jae-joon to step down, claiming it was absurd to just place the blame on a few junior officers.
Senior lawmaker Lee Jae-oh echoed this.
"Nobody will accept an attempt to fabricate evidence to create a spy. Such an attempt is as if the agency is rolling back the clock," he said on his Facebook account. "Nam should take responsibility for the controversy."
He further argued that the appeals court will ultimately decide whether Yu worked as a spy for Pyongyang.