"Michael D'Antonio is author of the book, " Never Enough: Donald Trump and the Pursuit of Success " (St. Martin's Press). The opinions expressed in this commentary are his. View more opinion articles on CNN.

(CNN) The American President has taken his gaslighter-in-chief world tour to Europe and is giving British Prime Minister Theresa May the full treatment. In his epically insulting interview with British tabloid The Sun -- owned by Trump ally Rupert Murdoch -- Donald Trump endorsed May's rival, Boris Johnson, and claimed that May ignored his advice and "wrecked" Britain's negotiations to leave the European Union.

Then, true to form, he claimed the on-the-record interview published by the paper was "fake news," and insisted that everyone accept that "I didn't criticize the Prime Minister."

May chose to play the adult as she joined Trump for a press conference. She calmly defended Britain's immigration policies, which Trump had attacked, and soberly reminded the world that "no two countries do more together than ours to keep their peoples safe and prosperous."

Careful where Trump is chaotic and mature where he is childish, May echoed the overall response offered by steadfast allies whom the President has offended on his European tour. Confronted by a man who sees life as a matter of fighting and likes to demonstrate his strength by picking on the less powerful -- even when they are friends -- May and the others are stepping out of the way to let Trump reveal the content of his character.

Ever since the 1980s, when New York Mayor Ed Koch descended to the gutter to fight with him over an ice skating rink in Central Park, it has been obvious that it's a mistake to mud wrestle with Donald Trump.

His whole method depends on proving that he's no worse than the people he smears, and he may be better because at least he doesn't pretend to have good manners. This tactic means that in the moment one descends to his level, the game is lost. However those who remain composed and calm can focus attention on Trump's ghastly technique.

Trump's first move in this by-now-boring game involves selecting a target who is obviously weaker than him. He is especially keen to go after people who are black, or brown, or female, or in any way less powerful, so he is guaranteed to "win."

At home, this inclination leads Trump to attack a black female member of Congress, Maxine Waters, as having as "low I.Q." and to hurl insults at Massachusetts Sen. Elizabeth Warren. It also may be what motivates him to separate asylum-seeking Latino mothers from their babies at the Mexico border and to attack a group of mainly black NFL athletes as " sons-of-bitches " because of their kneeling protests during the national anthem

In Europe, Trump has gone after two female leaders -- May, and German Chancellor Angela Merkel -- who are facing difficult political fights. In kick-'em-when-their-down style, Trump made a fatuous complaint that somehow Germany is "captive" to Russia due to energy imports from that country.

Like May, Merkel took the high road, saying "I myself experienced a part of Germany that was controlled by the Soviet Union, and I am very happy today that we are united in freedom as the Federal Republic of Germany. We decide our own policies and make our own decisions, and that's very good."

For Americans who have endured Donald Trump since the 2016 campaign, his pattern of conflict-creation is familiar. We know that his bluster is little more than hot air and that the best response is to remain calm and carry on. We also know to pay attention to the people Trump refuses to confront in a strong way. This list begins with Vladimir Putin.

Moscow's attacks on American democracy contributed to Trump's election win in 2016 and are the subject of the ongoing Mueller probe, which on Friday resulted in the indictment of 12 Russian military officers charged with engaging in a "sustained effort" to hack Democrats' emails and computer networks. Investigators continue to look into the Trump team's contacts with Russians. Meanwhile Putin gets the kid glove treatment from Trump.

Democrats are calling for Trump to cancel his planned meeting with Putin in Helsinki, on news of the indictments, but there is no indication that he will do so. We should note here that Deputy Attorney General Rod Rosenstein told reporters that he'd informed Trump of the impending indictments days ago -- and he made no move to alter his plans.

Indeed, during his visit to Europe our President has said he expects his session with him to be the "easiest" meeting he will have in Europe.

The most notable thing about Trump's regard for Putin is that fact that the Russian leader is, himself, a pariah whose country is isolated by sanctions and in desperate economic shape.

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The odious Putin should be viewed as weak and vulnerable, but Trump treats him with the kind of respect he reserves for the truly powerful. He's not America's friend, but Trump treats him like a buddy. It make one wonder what kind of friendly favors Putin may have done for Trump in the past and what he's holding over him now.