Wednesday’s election victory of opposition-backed civic activist Park Won-soon rocked the ruling party, added to President Lee Myung-bak’s woes, and rattled the country’s traditional two-party political landscape.

The 9 percentage-point gap in television exit polls piled pressure on the Grand National Party and the presidential office, already reeling from a series of setbacks including an opposition offensive on Lee’s purchase of property for his retirement and the bribery allegations of two of his closest associates.

“The voter turnout and voting tendencies among different age groups appear to have been the determining factors,” an aide to Lee said, urging people to wait until the vote count was completed.

Cheong Wa Dae did not make an official statement on the vote results.

The defeat to a political novice raised speculation of a larger-than-expected shakeup of Lee’s aides.

Lee’s chief-of-staff Yim Tae-hee held a meeting with senior presidential secretaries Wednesday afternoon to discuss the voter turnouts disclosed each hour by the national election watchdog and the directions of state affairs management for possible outcomes.

With this year’s major election cleared and Cheong Wa Dae flickering away from the center stage, the nation slipped into a new political phase for the 2012 presidential race.

The Seoul mayoral by-election provided an opportunity for presidential hopefuls to begin a warm-up for their own campaigns.

The GNP’s factional leader and former chairwoman Park Geun-hye drifted from her usual low-key mien to campaign for her party’s mayoral candidate. Park, who is supported by a third of the GNP lawmakers, has been regarded as the party’s strongest presidential contender ever since she lost to Lee in the intra-party competition for presidential candidacy in 2007.

In the liberal bloc, Moon Jae-in, late President Roh Moo-hyun’s chief secretary, made his official debut as a potential presidential candidate by serving as the joint chief of Park Won-soon’s campaign committee and leading the canvassing for the Democratic Party candidate for Busan’s East Ward chief. Sohn Hak-kyu, chairman of the DP and another presidential aspirant, also took to the forefront in the by-elections.

Celebrated professor and IT entrepreneur Ahn Cheol-soo dipped his toe into the political arena early last month by hinting at running for Seoul mayor. He didn’t -- five days later he said he would endorse Park Won-soon instead -- but in the intervening time he beat Park Geun-hye in approval ratings. Despite his denial of any wish to pursue a political career, Ahn continues to be the biggest potential threat to the former GNP chairwoman.

Lee now has to deal with the flack from an election defeat and the prosecutorial investigations of two of his aides for allegedly taking kickbacks in exchange for influence-peddling.

The prosecution earlier this month indicted Lee’s former top aide for public relations Kim Du-woo on bribery charges, concluding that he accepted cash, gift certificates and golf clubs worth a total of 130 million won from a lobbyist working for a corruption-ridden secondary lender.

Kim was asked to pull strings to ease regulatory inspections on Busan Mutual Savings Bank last year and get a Financial Supervisory Service official promoted early this year, the prosecution said. Kim continues to deny the charges. Sixty-five people have been indicted so far over the scandal surrounding the Busan savings bank.

Shin Jae-min, another Lee associate, also went under prosecutorial inquiry for spending nearly 100 million won ($90,000) with a corporate credit card provided by a businessman while serving as second and first vice culture minister in 2008 and 2009.

The Seoul Central District Court, however, denied arrest warrants for Shin and the self-proclaimed bribe-giver Lee Kuk-chul last week. State prosecutors plan further questioning of Shin and Lee, chairman of SLS Group, for evidence.

The latest blow to Lee was the criticism against his May purchase of a housing lot in a previously greenbelt area in Naegok-dong, Seocho-gu, under his son’s name.

Lee wobbled out of the controversy by deciding to nullify the purchase and return to his old home in Nonhyun-dong, Gangnam-gu, which his office earlier said was inept as the cost of additional land for security service did not meet the budget.

The presidential office had initially called for a state budget of 7 billion won for the purchase of additional plot around the Nonhyun-dong residence, which ruling and opposition legislators cut to 4 billion won last year.

Lee is bound for St. Petersburg and Cannes next week for summit talks with his Russian counterpart and the G20 summit, the first of his three overseas trips slated for November.

By Kim So-hyun (sophie@heraldcorp.com)