SEOUL, South Korea — The last time his liberal political party was in power, Moon Jae-in saw his boss at the time, Roh Moo-hyun, then South Korea’s president, walk across the Demilitarized Zone into North Korea for a summit meeting that resulted in a peace declaration and promises of massive aid.
He then saw those deals discarded a year later, in 2008, by a newly elected president who sought closer ties with President George W. Bush, who had branded the North part of an “axis of evil.”
Now, as president of South Korea, Mr. Moon is keen not to repeat past failures as he stakes his own political career on brokering a deal between the unpredictable leaders of the United States, his nation’s protector, and North Korea, long its mortal foe.
As chief of staff during the Roh administration, from 2003 to 2008, Mr. Moon did not participate in the negotiations with the North, led at the time by Kim Jong-il, the father of the current leader, or join Mr. Roh’s overland visit to Pyongyang, the North Korean capital. But he did help Mr. Roh organize those talks, held in October 2007.
He has clearly taken to heart what he sees as the lessons of that stillborn peace initiative.
One take-away was that advancing inter-Korean relations with generous offers of aid is a non-starter so long as the United States remained locked in a standoff with the North over its nuclear weapons program.
Another was that any deal with North Korea must be struck and implemented early in the terms of the South Korean and American presidents. This ensures the agreement does not die with a change of governments and political ideologies in Seoul and Washington, as the 2007 agreement and other past deals did.
“When we look back, the most important thing is speed,” Mr. Moon told the current North Korean leader, Kim Jong-un, during their meeting last week in the Demilitarized Zone, the fortified border separating the two Koreas.
During that meeting, Mr. Moon urged the North Korean to move quickly to make a deal with President Trump during their talks, expected later this month or next month. “We have to learn lessons from the past,” Mr. Moon told Mr. Kim.
That need for speed is apparent in the fast pace of diplomacy that appears to be leading to a first-ever summit meeting between the leaders of the United States and North Korea, who just a few months ago appeared on the brink of war.
Mr. Moon, 65, has played a key role in bringing together Mr. Trump and Mr. Kim, who now appear likely to meet at Panmunjom, the same “truce village” in the Demilitarized Zone where Mr. Moon held his talks with Mr. Kim.
Such a meeting would be a triumph for Mr. Moon, who has experienced both highs and lows in his country’s relations with North Korea.
Mr. Moon was a conscripted member of an elite paratroop unit in 1976, when axe-wielding North Korean troops murdered two American Army officers while they pruned a poplar tree that blocked their view at Panmunjom. In “Operation Paul Bunyan,” Mr. Moon’s unit was sent in to finish chopping down the tree while the North Koreans stood back.
Until last week, Mr. Moon’s only visit to North Korea was in 2004, when he accompanied his mother on a government-arranged reunion to see her younger sister for the first time since the Korean War. Mr. Moon himself was born in a refugee camp during the war, after his parents fled their native North Korea on board an American Navy cargo ship.
His approach to handling the United States is one of Mr. Moon’s biggest departures from his predecessor, Mr. Roh, who committed suicide in 2009 amid corruption allegations surrounding his relatives.
Mr. Moon appears to have concluded that Mr. Roh doomed his own peace deal at least in part by failing to get President Bush to back it. Instead, Mr. Roh, fiery and blunt, had vowed not to “kowtow to the Americans.”
Since taking office last year, Mr. Moon has shown himself more sophisticated and accommodating in managing relations with Washington.
He has closely consulted with the White House during the current rush of diplomacy. Mr. Moon has also been careful in public to credit Mr. Trump for making the current breakthroughs possible, saying that he deserves a Nobel Peace Prize.
The need to bring in America also reflects hard-earned domestic political lessons. Mr. Moon saw Mr. Roh and Kim Dae-jung, the two presidents who championed what was called the Sunshine Policy of engagement with North Korea, fail as the North persisted in its weapons programs despite generous aid.
Both died heartbroken men, with their legacy dismantled by their conservative foes, who ridiculed them as naïve and pro-North Korean.
“One thing South Korea has learned is that it cannot improve ties with North Korea without progress in denuclearizing North Korea,” said Kim Yong-hyun, a professor of North Korean studies at Dongguk University in Seoul. Otherwise, he said, any deal “would be like building a house cards.”
During his meeting with Mr. Kim at Panmunjom, Mr. Moon’s highest priority appeared to be convincing the young North Korean dictator that he could create a better future by striking a deal with Washington to rebuild his country’s economy in exchange for giving up his nuclear arsenal.
Despite the spectacle of the two Korean leaders leisurely holding hands as they stepped across their nations’ border, Mr. Moon and his aides compared his mission to “walking on this ice,” and urged Mr. Kim to quickly sign and implement a deal while he and Mr. Trump were in office.
“I am still in the first year of my term. I hope we can maintain this speed through my term,” Mr. Moon told Mr. Kim during their meeting.
Mr. Moon’s rush for an early deal is rooted in past experiences.
In 1994, North Korea and the United States reached their first of many agreements on dismantling the North’s nuclear program, then in its very early stages. Washington offered energy aid and promises of normalizing diplomatic and economic relations, but the accord unraveled after the United States dragged its feet because it did not expect the North Korean regime to survive long past the collapse of the Soviet Union.
North Korea also hedged its bets, secretly keeping a program to enrich uranium so it could one day build its own atomic bombs.
In 2000, President Kim Dae-jung, the initiator of the Sunshine Policy, flew to Pyongyang to meet with Kim Jong-il, ushering in a period of détente that seemed to promise an end to hostilities on the peninsula. Investment and trade flourished, and families separated by the war were allowed to hold reunions.
Kim Jong-il sent his trusted aide, Vice Marshal Jo Myong-rok, to the White House to ask President Bill Clinton to visit Pyongyang. However, Mr. Clinton decided he could not attempt so bold a diplomatic move at the end of his time in office, and instead sent his secretary of state, Madeleine Albright.
The new opening with Washington closed after President Bush took office in 2001. North Korea conducted its first nuclear test in 2006.
“After he stepped down, President Clinton visited Seoul and told President Kim Dae-jung how regrettable it was; he said if he had a little bit more time in office, he could have changed the course of the Korean Peninsula,” said Lim Dong-won, a former aide to Mr. Kim, who attended the meeting.
Mr. Roh, who replaced Kim Dae-jung, tried to keep the détente alive with his 2007 agreement on easing military tensions and increasing economic cooperation. But the deal, signed four months before Mr. Roh’s term ended, was quickly overturned by Mr. Roh’s conservative successor, Lee Myong-bak.
Mr. Lee was eager to align himself with Mr. Bush, who sought to isolate the North with sanctions in the hopes it would surrender its nuclear weapons program, a strategy continued by President Barack Obama.
So far, Mr. Moon’s gambit seems to be winning broad support within South Korea. Opinion polls show his approval ratings surging, with some nine out of 10 South Koreans viewing the DMZ meeting as a success.
Not all South Koreans are convinced, however.
Hong Joon-pyo, leader of the main conservative opposition Korean Liberty Party, likened Mr. Moon to former British Prime Minister Arthur Neville Chamberlain, who he said fell into Hitler’s “trap of false peace.”
“After being cheated eight times, did he still think for a ninth time that North Korea would not cheat this time?” Mr. Hong said.