What is one supposed to make of the “new furor,” as the New York Times put it, that has erupted over President Trump’s joke about Russia’s meddling in our presidential election? This thighslapper happened when the American leader sat down with the Russ strongman, Vladimir Putin, on the sidelines of the Group of 20 summit at Osaka and a reporter piped up to ask whether Mr. Trump would tell Russia not to meddle in American elections.

“Yes, of course I will,” Mr. Trump retorted. Then, as the Times related, the American president turned to the Russ leader and, “with a half-grin on his face and mock seriousness in his voice,” told him “Don’t meddle in the election, President.” Mr. Putin “smiled and tittered,” as the Times put it. At which point Mr. Trump pointed at another Russian “in a playful way” and said again, “Don’t meddle in the election.”

It’s long been our suspicion that in respect of Russia what so particularly horrifies the left here in America is the prospect that relations might improve in the post-communist era. We comprehend that Mr. Putin is a thug. He’s no more of a thug, though, than, say, such communists as Leonid Brezhnev or Mikhail Gorbachev. Yet our left was all for friendliness and detente with communist Russia. Or even peaceful coexistence.

Jimmy Carter, who is suddenly declaring Mr. Trump’s presidency to be “illegitimate,” was captured on film actually kissing the Soviet party boss, Leonid Brezhnev. That was when they met at Vienna. While in Vienna, as we heard the story told, Mr. Carter telephoned the Thai prime minister, General Kriangsak Chamanan, and asked him not to send back to Cambodia’s killing fields those fleeing the Khmer Rouge, only to be rebuffed because America was not yet willing to take them.

President Reagan, the American president who had the most profound understanding of Soviet communism, was a master at joking around with his adversary. He did that with Soviet party boss, Mikhail Gorbachev, when, in 1987, they signed the Intermediate-Range Nuclear Forces Agreement. Reagan showed an easy camaraderie, though he was the most hardline of any American president in respect of the Russ regime.

Veritable hilarity erupted in 1995, when, at Hyde Park, New York, President Yeltsin met with President Clinton to try to work out a deal in respect of Bosnia. Yeltsin got drunk at lunch and, appearing with Mr. Clinton, called the press a disaster. Mr. Clinton roared with laughter and clapped his adversary on the back, without a syllable of protest from the Democratic Party press.

That was before Secretary of State Clinton, then part of President Obama’s administration, met with the Russ foreign minister, Sergey Lavrov, and presented him with the famous “reset button.” The presentation was made with jocularity on both sides. Our own view is that humor is an essential element of most serious things, including diplomacy, and that, on this head, Democrats are in no position to compare themselves favorably to Mr. Trump.