President Trump’s descriptions of North Korean dictator Kim Jong Un included language that he usually reserves for himself.

Kim is “very talented,” Trump said at a news conference. Kim’s people have a “great fervor” for him — not entirely voluntarily — and Trump trusts him. Kim is a “rough guy,” but he is also “smart” and “wants a lot of good things” because he “loves his people.” Trump said he had a “great chemistry” with Kim. He would “love to have him at the White House,” but meeting him in Singapore was a “great honor.”

Such language is not unusual coming from a U.S. president when directed at long-standing allies, such as the leaders of Britain or Canada. It is highly unusual when directed at a longtime geopolitical adversary — much less one who has been accused of crimes against humanity for his regime’s treatment of its citizens. In part, that’s because the embrace of the American president, the leader of the free world, is a form of validation that can be used as propaganda by such regimes. As such, past presidents have broadly avoided such flattery.

In the wake of the Trump-Kim summit, Trump’s allies have been quick to note that other presidents have met with foreign leaders accused of violent, criminal acts.

The Barack Obama example, though, is instructive to the point above. President Obama met and spoke with Cuban leader Raúl Castro several times. Obama had a rote way of describing his interactions with Castro.

“I want to thank President Castro for the spirit of openness and courtesy that he has shown during our interactions,” he said in April 2015. The two had “both concluded … that we can disagree with the spirit of respect and civility, and that over time it is possible for us to turn the page and develop a new relationship in our two countries,” Obama said. Nothing about Castro being a beloved, talented leader.

In March 2016, Obama said, “President Castro, I want to thank you for the courtesy and the spirit of openness that you’ve shown during our talks.” Nothing about Castro or his brother Fidel being smart.

When Bill Clinton traveled to North Korea during Obama’s administration to help free two imprisoned journalists, North Korean media claimed that Clinton had apologized for their actions — a claim that was quickly denied by U.S. authorities. Clinton’s sitting for a photograph with Kim Jong Il, Kim Jong Un’s father, was criticized, including by pundits on Fox News. But Clinton offered no words of praise for the elder Kim.

(An aside: This comment from Sean Hannity about the Clinton visit seems worth highlighting. “I thought John Bolton had a great line,” Hannity said. “He said this comes perilously close to negotiating with a terrorist. And you know it’s a bad idea in terms — we should try to avoid, you know, negotiating with rogue states and terrorists, in general, and that it’s encouraging bad behavior.”)

When Ronald Reagan welcomed Indonesian dictator Suharto to the White House in 1982, he was more effusive. Suharto, as Erick Trickey noted in The Washington Post this week, had been involved in killing half a million Indonesians as he seized power, and of hundreds of thousands more when he annexed East Timor in 1975.

“I take particular pleasure in welcoming you and Madam Suharto to the United States and to the White House,” Reagan said when Suharto arrived. “And Mrs. Reagan joins me in extending personal hospitality on this important occasion. … As one of the world’s longest serving chief executives, indeed, as a senior statesman of Asia, your views on world affairs carry special authority and add special meaning to our discussions today. Your viewpoints and wise counsel will be greatly appreciated.”

“Once again,” Reagan said, concluding his remarks, “I welcome you, President Suharto, and you, Madam Suharto, in a spirit of friendship and respect. Mrs. Reagan and I are personally delighted with your visit.”

There’s one central difference with Kim: For decades, U.S. presidents had backed Suharto’s rise and presidency, seeing him as a bulwark against the spread of communism in Asia. He may have been a brutal dictator, but he was our dictator.

That mirrors Jimmy Carter’s praise of the Shah of Iran during a visit to that country in late 1977.

“Some have asked why we came to Iran so close behind the delightful visit that we received from the Shah and Empress Farah just a month or so ago,” Carter said. “After they left our country, I asked my wife, ‘With whom would you like to spend New Year’s Eve?’ And she said, ‘Above all others, I think, with the Shah and Empress Farah.’ So we arranged the trip accordingly and came to be with you.”

The “close friendship” between the U.S. and Iran — “an island of stability in one of the more troubled areas of the world,” per Carter — was “a good harbinger of things to come,” he said.

“This is a great tribute to you, Your Majesty, and to your leadership and to the respect and the admiration and love which your people give to you,” Carter said of that stability. Before the year was out, a popular uprising had begun.

When Richard M. Nixon visited China in 1972, an unprecedented visit for a U.S. president, he was more effusive about the activities he participated in than about the country’s leadership.

“The primary goal of this trip was to reestablish communication with the People’s Republic of China after a generation of hostility. We achieved that goal,” Nixon said on his return. “… we both realized that a bridge of understanding that spans almost 12,000 miles and 22 years of hostility can’t be built in one week of discussions. But we have agreed to begin to build that bridge, recognizing that our work will require years of patient effort.”

“I thought not only the ballet was great,” Nixon said while standing on the Great Wall, “… but I also thought that the athletic event last night was just superb. As you know, I have a rather casual interest in athletics, and it has been so reported. But the gymnastic events — I have never seen a tumbler like the last one. I have never seen that move made by a tumbler before.” He went on to praise the ballet for being “very dramatic,” including “having the gunpowder smoke float back into the audience so that we could smell it.”

One New York Times reader took issue with Nixon’s enthusiasm for the performance.

John F. Kennedy’s 1961 meeting with Soviet premier Nikita Khrushchev in Vienna was not a huge success, which certainly would have disinclined Kennedy’s wanting to shower his opponent with praise even had he considered doing so.

Instead, Kennedy reported that “Mr. Khrushchev and I had a very full and frank exchange of views on the major issues that now divide our two countries.”

“I will tell you now that it was a very sober two days,” Kennedy continued. “There was no discourtesy, no loss of tempers, no threats or ultimatums by either side; no advantage or concession was either gained or given; no major decision was either planned or taken; no spectacular progress was either achieved or pretended.”

He added that “neither of us tried to merely please the other, to agree merely to be agreeable, to say what the other wanted to hear. … Neither of us was there to dictate a settlement or to convert the other to a cause or to concede our basic interests.”

One of the more remarkable encounters between a U.S. president and a notorious foreign leader came in 1938, when former president Herbert Hoover sat down with Adolf Hitler. The New York Times reported on their private meeting.

“Former President Herbert Hoover appears to have given Chancellor Adolf Hitler at noon today the unusual experience of hearing doubt cast on the fundamental ideas of National Socialism and on the likelihood that it will be a successful system of government,” the Times said. “Mr. Hoover is reported to have pointed out to the Fuehrer that the American people do not believe that social progress is possible without intellectual liberty.”

Hoover, like other U.S. presidents, reserved his praise for Germans as opposed to their leader.

“Mr. Hoover answered by praising modern Germany’s technical and scientific accomplishments and referred briefly to his satisfaction at having been able to help the Germans to some extent in the hard years directly following the war,” the Times reported. (That post-World War I aid was … not what Hitler was hoping to see.)

Trump’s personal praise for Kim is itself highly unusual, particularly given the United States’ history with North Korea and given Trump’s interactions with the United States’ long-standing allies over the weekend.

Incidentally, during that March 2016 news conference in which Obama again thanked Castro for his “spirit of openness and courtesy,” Castro was asked his opinion on the 2016 presidential race in the United States. Which candidate did he prefer, Trump or Hillary Clinton?

Castro judiciously declined to respond.

This article was updated with Carter’s comments.