PARIS—The world leaders who met with Donald Trump on his Grand Tour of the Middle East and Europe over the last nine days may not have read Judah Grunstein’s essay in World Politics Review earlier this month, “How To Play the U.S. President—And Win,” but if not, their instincts and intelligence services gave them a good steer.

How else to explain Trump’s impression, apparently sincere, that the journey was a triumph? “Trip has been very successful. We made and saved the USA many billions of dollars and millions of jobs” he tweeted as he landed Friday in Sicily on the last stop of his journey, and, on Saturday as he took off: “Just left the #G7Summit. Had great meetings on everything, especially on trade where.... we push for the removal of all trade-distorting practices....to foster a truly level playing field."

In fact, earlier in Saudi Arabia and Israel, he opened the door to deepening and ever deadlier involvement in the Middle East, with the potential that either of those countries—tails that have been trying like hell for many years to wag the American dog—will start a war with Iran that Trump will feel he has to try to finish.

At the Vatican, in Brussels, and at the G7, while off-the-record comments chronicled a litany of contempt by his counterparts, and photographers captured images of a scowling pope, a downcast British Prime Minister Theresa May, a head-faking French President Emmanuel Macron, by and large the leaders seemed to be ignoring Trump’s schoolboy bully demeanor and execrable etiquette.

They got what they could get on a variety of subjects, listened to his bluster, let him pontificate about terrorism, his favorite theme, and agreed to let him ponder for another week at least the U.S. commitment to the Paris accord on climate change, as if he’d just begun to find out what’s involved and what’s at stake. Which may be the case:

Trump "came here to learn,” his economic advisor Gary Cohn told reporters at the G7 summit in Taormina, Sicily. “He came here to get smart. His views are evolving... exactly as they should be."

All the other leaders were presumed to be smart before they took office. Every one of Trump’s counterparts, even 39-year-old French presidential ingenue Macron, have years more experience in government than he does. All have better manners. And, all were playing by what we might call Grunstein’s Rules:

Come bearing gifts: Trump wants people to believe, and probably wants to believe himself, that he will always get the better of any negotiation, and always in the cause of “America first!” So, as Grunstein says, “the most important thing a savvy world leader should bring to [a] first meeting or interaction with Trump is an initial token concession.” China’s leader, Xi Jinping, set the standard for this, promising deals already arranged under the Obama administration, or vowing currency concessions over chocolate cake at Mar-a-lago that already are being rescinded.

The Saudis offered rather more substantial payouts: hundreds of billions of dollars supposed to be invested in American arms and American infrastructure, but such promises have proved evanescent in the past. And of course they come with a quid pro quo: the demonization of Iran and the Shia; the willful obliviousness to the role of Sunni fundamentalism aiding and abetting al Qaeda and the so-called Islamic State.

In many cases, says Grunstein, who is the editor in chief of the Paris-based World Politics Review, the largess directed at Trump need not be so grand, “Window dressing will do, preferably something that can be expressed in 140 characters.”

Keep It Simple, Stupid: “The KISS acronym here serves a dual purpose,” writes Grunstein in a particularly biting paragraph. “Trump is notoriously detail-averse and unabashedly uninformed. So visiting leaders should not expect a deep understanding of the relevant issues, or even a superficial familiarity with them, nor should they seek to engage him on a granular level of policy. Instead, they should focus on building a personal rapport. Trump’s confident and narcissistic public persona hides deep insecurities and a brittle ego. Whereas Barack Obama famously avoided personal connections with most of his fellow world leaders, Trump seems to crave their acceptance, to the point of clinging to imagined friendships with them. Obama was all business, man; Trump is a businessman, but a needy one in search of affection.”

This rule was followed as rigorously as possible by virtually all the leaders Trump met, including the pope. He even emerged from his meeting with Macron, who defeated Trump’s favorite in the French elections, seeming to think they had gotten along famously.

It’s complicated: The new American president has said pretty frankly in a number of interviews that all this foreign policy stuff that looked so simple from the outside of the tent, is a whole lot more delicate and dangerous when you’re really in the thick of it. He’s also discovered, as Grunstein writes, that the United States actually needs the cooperation of a wide range of countries to achieve its objectives. “So once the gift-giving and rapport-building are out of the way, a smart leader will find an opportune moment to explain the reality of the situation, highlighting how much he or she wants to help out, but how difficult that actually is.”

This seems to have been the process at work on the issue of NATO “dues,” which are not dues to the organization at all, but targets for domestic defense spending as a portion of gross domestic product. Even addressing the other leaders in Brussels, after what must have been many briefings about this, Trump seemed to think this issue could be described as if it were tardy membership fees at one of his golf clubs. The other leaders listened, vowed to make their 2 percent of GDP targets by 2024, as they had committed to do when Barack Obama was president, and hoped that Trump’s views would continue to “evolve” enough to save the most important strategic alliance the United States has.

Climate change was the other “explainer,” with Pope Francis trying to get Trump to recognize the obvious validity of climate science and the need to act on its rational conclusions. (Americans may be surprised to know how much more faith in science the pope has than POTUS, but there you go.) And the message was reiterated at Taormina by the leaders of Germany, France, Italy, Japan, Canada, and the United Kingdom, whose final communique was a united show of support for the Paris accord.

Trump told them as he told the pope, that he’d think about it. Evolving. Evolving …

Work the refs: Grunstein suggests the American president's outrageous ad libs and Twitter storms "are Trump’s way of working off steam, and it’s a mistake to respond to them directly or even to take them that seriously. Smart leaders will instead find the influencers in Trump’s entourage and the relevant arguments most likely to shape his opinion, and make their case with them. This means getting creative; anyone who is still calling the relevant desk at the State Department hasn’t been paying attention.”

Son-in-law Jared Kushner would be an obvious go-to guy. (And that's obviously what the Russians figured.) And it was not for nothing that German Chancellor Angela Merkel invited presidential daughter Ivanka Trump to a conference in Berlin a few weeks ago.

Work the phones: “Refusing to buckle in the face of Trump’s threats is easier when it is presented to him as a common position. This is likely to become more effective with time, as Trump seems to be realizing that a zero-sum pursuit of his America First agenda is actually a recipe for an America Alone world.”

Viz the climate change declaration by the G6 up again the American G1.

“The entire discussion about climate was very difficult, if not to say very dissatisfying,” Merkel said as Trump flew off. “There are no indications whether the United States will stay in the Paris Agreement or not.”

But the Big Six were not about to back down. As Macron told the French weekly newspaper Journal du Dimanche, alluding to his now famous death-grip photo op with Trump in Brussels, "My handshake with him, it wasn't innocent." Tweaking Grunstein's rule one, Macron said, "You have to show you're not going to make little concessions, even symbolic ones, but not play them up too much in the media either."

As the JDD noted, those white knuckles and that look straight into the eyes of POTUS were conscious markers. "Donald Trump, the Turkish president, or the Russian president operate in the context of power relationships, and that doesn't bother me. I don't believe in diplomacy based on public invective, but in bilateral dialogues I don't let anything pass. That's how you make yourself respected."

So the six held firm: “The United States of America is in the process of reviewing its policies on climate change and on the Paris Agreement and thus is not in a position to join the consensus on these topics,” read the final communique out of Taormina. “Understanding this process, the heads of state and of government of Canada, France, Germany, Italy, Japan and the United Kingdom and the presidents of the European Council and of the European Commission reaffirm their strong commitment to swiftly implement the Paris Agreement,” it added.

The bottom line on the G6 side was basically, "We understand you Mr. President, but you need to understand us. You need a little time? Okay. But every move you make tells us we're going to have to learn to get along without you."

This was also the gist of an extraordinarily vituperative editorial in Germany's Der Spiegel late in the week, which argued that Trump is a danger to the world and has to go, but probably won't. The only alternative: "The international community wakes up and finds a way to circumvent the White House and free itself of its dependence on the U.S."

Manage expectations: “Forestalling radical upheaval," writes Grunstein, "is about the best any world leader can realistically hope for. Trump is temperamentally volatile and capricious, and would be hard-pressed to focus his attention long enough to reach major deals that require steady leadership and patient stewardship. Moreover, as a weak president who has had difficulty passing legislation despite enjoying a majority in both houses of Congress, he cannot be counted upon to deliver anything that requires congressional approval. That means that key areas of cooperation and major landmark deals are likely to stall during his presidency. Instead, avoiding worst-case scenarios should be considered a major victory.”

“Following these simple steps will allow any world leader to emerge smiling from a meeting with Trump,” Grunstein wrote in a particularly prescient conclusion. “Unfortunately, it will be a smile of relief rather than satisfaction. Real progress will be hard to come by, and any victories will likely be Pyrrhic—for the United States and the world.”

This article was updated Sunday, May 28, at 4:15 EDT to include French President Emmanuel Macron's comments to the Journal du Dimanche.