In the latest local elections held Wednesday, the ruling party won 14 out of the 17 major races for top administrative posts in provincial and metropolitan city governments, showed ballot counting by the National Election Commission.
The number more than doubled from six gubernatorial and mayoral posts held by the Democratic Party prior to the elections.
The main opposition Liberty Korea Party ended up only with two such posts, down from six it previously held.
Such an unprecedented victory is widely expected to give the ruling party nearly a total control over regional governments.
The president has been moving to increase the autonomy of local governments since taking office in May 2017 as part of his efforts to decentralize power.
He even sought to give local governments the right to set their own tax rates to a certain extent in a constitutional revision that has been blocked by opposition parties.
However, increased autonomy of local governments also often meant increased resistance against government policies, especially from local governments headed by opposition leaders.
With Democratic Party heads of major provincial and metropolitan city governments now outnumbering those from the LKP 14 to two, Moon will likely face little or no opposition at least from local governments.
"With the president's approval rating remaining so high and the sweeping victory in the elections, there now remains little possibility for any new political maneuver," a ruling party lawmaker said, while speaking on condition of anonymity.
Moon's approval rating has mostly stayed over 70 percent since he took the top executive office.
The ruling party's victory in Wednesday's elections partly confirms Moon's high approval rating, and will likely further expand the public's support for the president and his policies, including his North Korea policy.
"We simply did not have the strength to fend off (the president's) peace offensive," said Sohn Hak-kyu, a senior election campaigner for the minor opposition Bareunmirae Party, blaming the administration's ongoing dialogue with North Korea for the party's humiliating defeat in the latest local and parliamentary by-elections.
The Bareunmirae Party, currently the third-largest party in the unicameral National Assembly, even failed to take any of the 226 top administrative posts at district governments throughout the nation, only producing one local councilor out of the possible 737 in 226 districts.
The Democratic Party also clenched 11 out of 12 parliamentary seats up for grabs in the by-elections, only losing the remaining seat to the LKP in Gimcheon, North Gyeongsang Province, where the ruling party had no candidate.
It especially marked a great victory for the ruling party in that only three of the 12 National Assembly seats had previously been held by its lawmakers.
The Democratic Party now controls 129 seats in the 299-seat National Assembly, widening its gap with the LKP to 15 from five.
The 129 seats are still short of a majority, but the increase will certainly give a significant boost to the president.
"The result of the elections can be called a great victory for the ruling bloc but also a public judgment against the opposition bloc, which has done nothing but oppose whatever the Moon Jae-in administration did and shackle the government since the administration took office," a ruling party official said.
LKP chief Hong Joon-pyo was already expected to step down, along with Rep. Yoo Seong-min, a co-head of the minor opposition Bareunmirae Party, the two political heavyweights who have also been most critical of Moon and his administration.
"We will take our victory as the people's approval of our direction so far, as well as their mandate to continue moving in that direction," the ruling party official said.
The president himself acknowledged the outcome of the latest elections will give his government a "great strength."
"The people have given the government a great strength. The support the people have shown feels heavier than ever after learning that the turnout rate was the highest in 23 years for local elections," Moon said in a statement read on his behalf by Cheong Wa Dae spokesman Kim Eui-kyeom.
Still, he said he understood the victory did not mean public approval of all government policies.
"I am well aware of the fact that the support does not mean overall approval of state management. They have shown us their faith though there must be many areas they are not happy with. That is why I am more grateful and more sorry," the president said.
"I will once again clear my mind. I will try harder. I will especially remain vigilant so I will not be complacent about the outcome of the elections or be indolent," he added. (Yonhap)