LONDON (BLOOMBERG) - Mr Donald Trump's combative new foreign policy team should look at two precedents as the US president pursues summits with the leaders of Russia and North Korea, according to former diplomats and historians. One is now considered a historic success, the other an unmitigated disaster.
Negotiations between Mr Ronald Reagan and Mr Mikhail Gorbachev in Reykjavik in 1986 helped reverse the nuclear arms race and usher in an end to superpower confrontation.
An earlier encounter in 1961 between Mr John F. Kennedy and Mr Nikita Khrushchev in Vienna came close to causing World War III.
With a stalled arms-control regime, a broken US-Russian relationship and peace on the Korean peninsula at stake, Mr Trump's meetings could help dictate whether the world slides further back toward the days of missile proliferation and proxy conflicts.
Incoming National Security Adviser John Bolton, who was named to the post last week, and CIA Director Mike Pompeo, Mr Trump's pick for Secretary of State, have called for regime change in North Korea and are hawks on Russia.
No firm dates have been set for the sit-downs with Russian President Vladimir Putin and North Korean leader Kim Jong Un and it remains uncertain that they will take place.
Yet should they happen, Mr Trump has already shown he can go off-piste, and therein lies the risk, according to Professor of International History David Reynolds at Cambridge University.
"The two summits are really good examples of how these kinds of relatively unscripted meetings can go either very well, or very badly," said Prof Reynolds, author of "Six Meetings that Shaped the 20th Century".
Given Mr Trump's unpredictability "it could be a shouting match with 'Rocket Man', or it could be a breakthrough" on an issue that has frustrated successive US presidents, he said.
Whoever prepares Mr Trump for the summits, the key is to learn the lessons of Vienna, said Prof Reynolds. There, Kennedy arrived ill-prepared, with a rigid position, and let himself be drawn into long and bruising historical arguments. The best advice is to be clear and realistic about what you can hope to achieve, said Prof Reynolds.
In contrast, the Reykjavik summit ended without agreement and was initially called a failure, but it paved the way for major arms control agreements and the end of the Cold War, according to Mr Ken Adelman, who in 1986 was the director of the US Arms Control and Disarmament Agency and was among Mr Reagan's advisers at the meeting.
Mr Reagan's positions at the summit furthered his clear twin goals of reducing the nuclear threat and defeating communism, he said.
"To me the big lessons of Reykjavik are, number one, to make no small plans," said Mr Adelman. "The idea is to think big when you have an opportunity like this, and Reagan and Gorbachev really thought big. The second thing is to figure out how to get from here to there, which Reagan did," he said.
Mr Trump's aims with regard to Mr Putin remain uncertain amid the swirl of allegations of collusion with Russia during his election campaign and wide disparities between his dovish rhetoric at the time and tough American policies since.
The US is likely to announce on Monday (March 26) the expulsion of dozens of diplomats in response to the recent nerve-gas attack on a former Russian spy and his daughter living in Britain.
Former Russian diplomat Vladimir Frolov predicts that the Trump-Putin summit would be another Reykjavik in terms of tone.
"They will sweet-talk Trump," he said. "Putin's only chance is to manipulate Trump when they're talking face-to-face." Still, "there's no reason to expect breakthroughs", said Mr Frolov. "Trump won't be allowed to sell everything in the American supermarket to Putin in one sale."
What the Cold War meetings and Mr Trump's potential ones have in common is an open agenda and lack of the painstaking months of diplomatic preparation that precede summits with more formal, treaty signing goals.
That makes personal chemistry more important, and the outcome less predictable, said Mr Nikolai Sokov, a former Soviet and Russian nuclear arms negotiator.
In such unstructured meetings, "things happen, things can go wrong", especially if - like Mr Trump or Mr Khrushchev - either party likes to negotiate by raising the stakes and making high level threats, he said.
Mr Reagan's aides prepared him for Reykjavik with a video, rather than a briefing book they knew he would not read.
Mr Trump did not read instructions for a phone call not to congratulate Mr Putin on his election victory this month and went ahead anyway.
Yet, lack of attention to detail and refusal to follow script does not have to be disastrous, according to Mr Sokov, now a senior fellow at the James Martin Centre for Nonproliferation Studies in Monterey, California.
"The important thing in Reykjavik was that both parties wanted to reach an agreement and had a strong personal relationship, so even though they failed and went home, Reagan and Gorbachev could then go back to the same dialogue they'd had before the summit," he said.
"In the case of the Trump-Kim summit, however, there is nothing to return to. Instead, failure could mean war."
Few analysts believe Mr Kim is ready to give up his nuclear arsenal. Any diplomatic solution would likely have to involve a carefully choreographed compromise of the kind made with Iran in 2015, Mr Sokov said. That is a deal Mr Trump and his new national security team want to tear up.
The risks of a bust-up would appear high if Mr Bolton was chosen to run the National Security Council ahead of the meeting with Mr Kim. In recent months, Mr Bolton has advocated a pre-emptive strike against North Korea's nuclear arsenal and a take-over of the North by South Korea.
"How do you know the North Koreans are lying? Because their lips are moving," he told Fox News on March 9.
In Vienna, there was virtually no prepared agenda or personal relationship between the US and Soviet leaders at all. Mr Kennedy and Mr Khrushchev faced down each other over the divided status of Berlin and closed their meeting with mutual threats of war.
Mr Trump's goal for North Korea - nuclear disarmament - risks proving as incompatible.
The much younger Mr Kennedy confided later that he had allowed himself to be browbeaten, and that Mr Khrushchev concluded he was weak. The construction of the Berlin Wall, the Cuban missile crisis and the Vietnam war followed.
"Vienna was more like a test to see what this guy is about: They didn't trust each other and it didn't work," said Mr Sokov. "That could be a good example for what we see with Trump and Kim."