Anything can happen in Presidential politics – take, for instance, the United States – but it is all but certain that Moon Jae-in, a persistent anti-government foe, will be elected South Korea’s president Tuesday to succeed the acting president, Hwang Kyo-ahn, standing in for the impeached Park Geun-Hye.

In the seventh presidential election since adoption of the "Democracy Constitution" 30 years ago, Moon holds an overwhelming lead in the polls over the centrist People’s Party founder Ahn Cheol-so and the conservative Liberty Korea Party candidate, Hong Jeon Pyo. (Hwang, also prime minister, declined to run.)

Left, or liberal or progressive, as his adherents prefer, Moon at 64 has a historic opportunity to bring North and South Korea to terms while moderating disparate political forces in the south. Forecasts of success in attaining these extremely difficult goals, however, would be premature.

All that’s certain is that Moon represents a desire among his countrymen for change, for a departure from confrontation with North Korea, for an end to endemic corruption that destroyed the previous government – and for the rights of millions strangled economically by the multi-tentacled chaebol or conglomerates.

He enters the Blue House, empty since the arrest and ouster of Park nearly two months ago, with a mandate that some Americans fear may undermine the US-South Korean alliance that has defended the South since Korean War. As one former senior American diplomat told me: “We are headed for serious trouble.” Indeed, he added, “It’s unavoidable.”

Or is it? Moon, a former lawyer on behalf of workers and victims of human rights abuses, has also said he supports the US-Korean alliance, and he’s denounced as false or distorted a report that he once said he would visit North Korea’s leader Kim Jong-un before going to Washington.

In fact, Moon has made it clear that he would love to explain himself and his outlook as soon as feasible after his election. That’s enough for leftists – real leftists, not simply left-leaning liberals – to say, in effect, Look, he’s already compromising.

Moon has upset the leftists who organized and led the candlelight vigils of hundreds of thousands of people that helped bring down the Park government by failing to go along with demands and claims that are central to their campaign against conservatives.

They accuse him, as one posting put it, of being “spineless” for accepting the official view that a North Korea torpedo sank the South Korean navy corvette Cheonan seven years ago, with a loss of 46 sailors’ lives, not an “old American mine,” a theory that is an article of faith among pro-Northers. And he has also upset leftists, spurred on by the country’s biggest labor union, by failing to come out totally against THAAD, the Terminal High Altitude Area Defense counter-missile battery that’s now “operational,” in the parlance of a US spokesman, south of Seoul.

From day one, Moon will be watched for his every expression, every utterance about THAAD. Yes, he’s said Park as president should not have acceded to American arguments on the need for THAAD to shoot down high-flying North Korean missiles and that the National Assembly should have been able to vote on the wisdom of having it there. No, now that it’s in place, despite persistent noisy anti-THAAD demonstrations, he has not said that he would demand its removal.

Whatever Moon says or does about THAAD, the issue will test policy toward the US and China. Ok, Moon should have no problem ignoring the US$1 billion bill that President Trump says Korea owes for THAAD. The outgoing conservative government has already repudiated it, saying the bill is covered by a previous agreement, and Americans at all levels agree.

Moon will have more trouble, however, dealing with China, which has punished South Korean industry by rigid customs and safety inspections, cutting off lucrative group tours of Chinese to Korea, and shutting down Korean-owned factories and stores. No Korean chaebol has suffered more than the Lotte empire, which has had to close most of its Lotte Mart outlets in China for the unpardonable sin of surrendering a golf course for the THAAD battery.

The Chinese, just to show they aren’t such bullies after all, may eventually relent even though they say the real reason the Americans want THAAD in Korea is the extraordinary radar gear it’s got to track down China’s own missiles. Get used to it, Koreans are telling Chinese. It’s there so forget about it.

The North Koreans will not be so understanding. Moon might well like to visit Pyongyang, as did the liberal Roh Moo-hyun near the end of his presidency in 2007. Moon, as Roh’s chief of staff, was with him when he met Kim Jong-il, but Kim Jong-un, who took over after his father’s death in 2011, may not be eager to invite him. Rather, Kim may want to test his desire for reconciliation, to see how he reacts to missile shots – if not a sixth nuclear test – and, above all, how he responds to the blandishments of U.S. diplomats and military officers.

It’s possible that Moon, like Roh, will choose to upset the Americans by proving, as he has promised during his campaign, not to be their yes-man. That may be easier said than done, however, considering the depth of US military and diplomatic ties to South Korea, the tightness of the alliance and the multitude of interlocking bonds under the aegis of a “combined command” led by the US military commander in Korea.

Moon, however, will have to be mindful of the constituency that managed, non-violently, to end nine years of conservative rule since the election of Park’s predecessor, the former Hyundai executive, Lee Myung-bak, in 2007.

In the first months of his presidency, Koreans will be transfixed by the trials of Park Geun-hye and a raft of confederates, notably her long-time bosom buddy Choe Sun-sil, the Rasputin-like figure whose hold over her led to charges of massive corruption involving two foundations.

They’re all in jail, held without bail, including the top Samsung executive, Lee Jae-yong. On Lee’s case hangs the issue of government-chaebol relations. He’s accused of making donations that were bribes to ease the merger of two companies through which he figures to take over the empire from his ailing father, comatose since a massive heart attack three years ago.

Will Moon, in the interests of moderation and all-around good-will, follow the example of his predecessors and issue pardons, or suspend sentences, against most of if not all the 30 accused miscreants?

A devout Catholic, Moon will be under intense pressure to follow the biblical injunction, “Get rid of all bitterness, rage and anger, brawling and slander, along with every form of malice” – rather, “Be kind and compassionate…forgiving each other.”

To which those who campaigned most passionately for change might respond, “The more things change, the more they stay the same.”

Donald Kirk is a longtime Korea watcher and regular contributor to Asia Sentinel