SEOUL, South Korea >> A possible South Korean presidential contender said Thursday his country should reconsider plans to deploy an advanced U.S. missile defense system to cope with North Korean threats, a move Washington is likely to see as disruptive.

Liberal opposition politician Moon Jae-in said the security benefits of having Terminal High-Altitude Area Defense, or THAAD, would be curtailed by worsened relations with neighbors China and Russia. He downplayed concerns that South Korea backtracking on the plans would cause tension with the United States, which he said was the “most important country” for South Korea in face of nuclear-armed, rival North.

“The issue of whether or not to deploy THAAD should be pushed to the next government,” Moon said in a news conference.

“Reconsidering THAAD would have to be preceded with diplomatic efforts, including diplomatic efforts with the United States. I don’t think that the reconsidering of THAAD would harm the South Korea-U.S. alliance,” he said.

Recent opinion polls have shown Moon as a presidential favorite amid the popular anger over conservative President Park Geun-hye, whose powers were suspended after lawmakers last week voted to impeach her over an explosive corruption scandal.

South Korea’s Constitutional Court has up to six months to decide whether Park should permanently step down. If Park is formally removed from office, the country would hold a presidential election within 60 days.

Moon, who conceded the 2012 presidential race to Park, said he expected the court to rule on Park’s impeachment sometime between late January and early March, setting up a presidential election around April or May.

“It would be a huge honor for me if I can take part in the next presidential election,” Moon said.

South Korean military officials in September picked a private golf course in the country’s southeast as the site for THAAD, which was slated to be deployed by the end of next year. They originally chose a nearby artillery base in the rural farming town of Seongju as the site for the system, but changed locations following fierce protests from locals who expressed concern over potential health hazards they believe the system’s powerful radar might cause.

The plan to deploy THAAD in South Korea has angered not only North Korea but also China, which suspects that the system would allow U.S. radar to better track its missiles. Russia also opposes the deployment.

Moon also argued that Seoul should put dialogue over sanctions in persuading Pyongyang to give up its nuclear ambitions. He rated the Park government’s hard-line stance against North Korea as a “complete failure” because it “didn’t function in any way” to prevent the North from expanding its nuclear weapons and missile programs.

“It has been confirmed that pressure and sanctions alone would not be enough to influence North Korea to give up on its nuclear weapons,” said Moon, calling for a “two-tack approach” of sanctions and talk.

“We need strong punitive measures against North Korea’s nuclear tests and missile launch tests, but the purpose of such strong pressure and sanctions should be bringing North Korea to the negotiation table for denuclearization.”

Moon, a former human rights lawyer and aide to late liberal President Roh Moo-hyun, also pledged to fight income inequality and push business reforms to curb excesses of “chaebol,” or family-owned conglomerates that dominate the country’s economy, to create a level playing field for smaller companies.

The opposition Democratic Party’s primaries could shape into a showdown between Moon and Lee Jae-myung, the outspoken mayor of Seongnam city whose popularity rose rapidly in recent months amid rage over the Park scandal.

The conservatives appear to be pinning their hopes on outgoing U.N. Secretary-General Ban Ki-moon after Park’s scandal complicated politics for her Saenuri Party. In a visit to South Korea in May, Ban told reporters that he would “think hard about what to do as a citizen” after he returns home on Jan. 1, which was seen by the local media as a clear hint on a presidential bid.