Peace on the Korean Peninsula.
After decades of bloodshed and strife, including a runup to the Olympic Games that saw the rival Koreas lurching toward war amid a near-constant barrage of North Korean missile and nuke tests, it's such a ludicrous concept at first glance that many refuse to even consider it.
Not South Korea's liberal president, Moon Jae-in, a true believer in the power of Koreans talking to Koreans when it comes to solving the woes that have beset the Korean Peninsula since it was divided in 1945.
Moon has always harbored dreams of rapprochement, even as the missiles flew during his first months in office and he was forced to take a hard line during a deepening standoff featuring the South, his American ally and his northern neighbors.
Now, with an invitation to meet the North's dictator in Pyongyang, personally delivered on the sidelines of the Pyeongchang Olympics by that dictator's sister during the first-ever peacetime visit to the South by a member of the North Korean ruling family, Moon may be on the brink of a legacy-defining moment. If he's not actually forging peace, he's at least putting himself in a position to make a serious assault on the notion.
"Dizzying" is how one South Korean newspaper described the diplomatic typhoon swirling over the Korean Peninsula, with all the big players seemingly wanting different things and Moon, at times, the only calm in the storm.
The son of North Korean refugees and a leading advocate of a previous liberal government's "Sunshine Policy" of engagement with the North, Moon has spent his career — a lifetime, really — waiting for this chance. The question now is whether he can persuade the North Koreans, his own people and Washington to back his play.
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Of the three, the North Koreans might be the easiest sell.
Moon has not yet formally accepted the invite, and Washington would probably rather he not visit Pyongyang until the North puts its nukes on the negotiating table. Many South Koreans, meanwhile, who have been threatened with war for decades and saw 50 of their citizens killed in attacks blamed on North Korea in 2010, will be deeply wary of any deal that does not provide real security.
Moon knows the risks. He has taken a cautious approach to the invitation thus far, but the rivals' lightning-quick swing from antagonism to seeming affection could be a chance too tempting to pass up.
The first liberal president in a decade, Moon has repeatedly said since his election in May that he'd be willing to visit Pyongyang and meet with Kim Jong Un if that would help solve the North's headlong pursuit of a nuclear arsenal that can target the U.S. mainland.
It's difficult to find an exact historical comparison to Moon's situation outside of Korea. It's not Nixon's stunning visit to China; it's not Reagan urging the Soviets to tear down the Berlin Wall. Perhaps the best comparison is to the man who Moon has called his "destiny," and whose North Korean policy Moon is forever linked to: The late liberal president, Roh Moo-hyun.
Moon was raised in poverty in Busan by North Korean parents who'd fled during the war. He was imprisoned as a young man for working to topple South Korea's military rulers and forced into the elite special forces as punishment. Stopped from becoming a judge because of his student activism, he became a human rights lawyer at a time where that work held real risk.
His boss was Roh Moo-hyun.
When Roh became president in 2003, Moon's influence with his mentor got him the nicknames "King Secretary" and "Roh Moo-hyun's shadow."
Moon helped Roh on the "Sunshine Policy" begun by the country's first liberal president, Kim Dae-jung, the Nobel Peace laureate and former political prisoner, in the late 1990s. Roh continued the efforts, which saw North and South Korea pursue now-stalled economic cooperation projects and reunions of families separated since the 1950-53 Korean War, which ended with an armistice, not a peace treaty.
Moon oversaw Seoul's preparations for the 2007 inter-Korean summit talks, only the second-ever such leadership confab, between Roh and Kim Jong Il, the late father of Kim Jong Un.
A decade of conservative rule, beginning in 2008, overturned the policy. Now Moon, while not lobbying for its return, clearly wants to engage the North.
Among the hurdles to a deal in 2018 is the North's steadfast claim that it is an already-established nuclear power and that its bombs are not open for negotiation.
Moon's defenders point out that he has, for the most part, fallen in line with the international effort, led by Washington, to isolate and sanction the North for its ICBM launches and nuclear test over the last year. Many think he'll take a cautious approach if a summit comes off, given the nuclear threat.
Moon has benefited from the rock star-like reception that Kim Jong Un's sister, Kim Yo Jong, has received here. Her picture, often with a bemused half-smile, has been splashed across newspapers. Seemingly every aspect of her appearance and demeanor has been examined with microscopic detail on TV.
Her visit may "open the gates wide" for talks between the Koreas and contribute to regional peace, according to an editorial in the liberal Kyunghyang Sinmun newspaper.
The conservative Dong-A Ilbo warned that South Korea may lose the trust of the United States and Japan as it courts North Korea for talks, and that the North, knowing that Seoul and Washington plan to resume war games in March, "may deploy a strategy of using the Moon Jae-in government as a shield from the United States."
"The current state of the Korean Peninsula is so dizzying because South Korea, North Korea and the United States are each thinking too differently," the newspaper said.
It seems likely that those twin possibilities — the political opportunity of a lifetime coupled with intense distrust of North Korean intentions — played in Moon's mind when he raised a toast at a lunch Saturday with Kim Yo Jong.
"The occasion today is watched closely by the world, and there's a lot of hope placed on the South and North," he said. "I feel that weight on my shoulders."
By the beaming smile Moon gave his rival's sister, you could hardly tell.
Foster Klug, South Korea bureau chief for The Associated Press, has covered the Koreas since 2005. Follow him on Twitter at @apklug.