There is every reason President Trump should not have hosted President Recep Tayyip Erdogan of Turkey at the White House, including Turkey’s attack on America’s Kurdish allies in Syria, its purchase of antimissile systems from Russia and the brutal continuing crackdown on Turkish journalists and opposition figures. That was obvious to legislators from both parties who wrote Mr. Trump, urging him to disinvite Mr. Erdogan, and it was no doubt obvious to most members of Mr. Trump’s administration, who are now scrambling to justify the visit as bridge-building to a critical ally.

But in Mr. Trump’s world — the world we are increasingly living in — Mr. Erdogan is “a tough guy who deserves respect.” In fact, the tougher the guy, the more respect Mr. Trump seems prepared to show, whether it’s a secretive tête-à-tête with the Russian president, Vladimir Putin, in Finland, meetings with North Korea’s Kim Jong-un or protestations of admiration for Xi Jinping of China and Rodrigo Duterte of the Philippines.

There are probably many ways to explain this weakness for ruthless authoritarians, including the affinity of a real-estate wheeler-dealer for men who have the power to deliver what they want — something American democratic institutions have often blocked Mr. Trump from getting. In any case, the real question is not what drives Mr. Trump, but whether his dealings with the tough guys benefit the United States in the way that Cold War relations with the Soviet Union or China were believed to lower tensions or improve lives in police states.

At the joint White House news conference Wednesday, Mr. Erdogan showed little reciprocity for Mr. Trump’s bonhomie, making no pretense of taking seriously Mr. Trump’s famously fatuous Oct. 9 letter (“Don’t be a tough guy. Don’t be a fool. I will call you later.”). And hearing Mr. Trump praise him did not prevent Mr. Erdogan from raising pet peeves against the United States, including the vote in the House of Representatives to recognize the killing of an estimated 1.5 million Armenians in Ottoman Turkey as “genocide,” or the refusal of the United State so far to extradite Fethullah Gulen, a rival Mr. Erdogan holds responsible for a failed coup in 2016.