The most revealing moment in the presidential candidates’ first joint forum Wednesday night came when Donald Trump told the world how much he admires Vladimir Putin .

Never mind that the Russian strongman invaded Ukraine and seized Crimea. Never mind that he supports the butcher Bashar al-Assad in Syria. Never mind that so many of his political opponents end up murdered or imprisoned. Never mind that U.S. officials suspect his government of trying to disrupt our election with cyberattacks. In Trump’s star-struck eyes, all of this makes him “a leader, far more than our president has been a leader.”

Putin, you see, once paid Trump a compliment. “If he says great things about me,” Trump told moderator Matt Lauer, “I’m going to say great things about him.”

There you have it, folks, the distilled essence of Trump’s disgraceful campaign. It’s not about immigration or foreign policy or making America “great again,” whatever that means. It’s entirely about Trump and his raging egomania.

Trump is sincere when he expresses preening self-regard. All the rest is just verbiage tossed with a light vinaigrette.

On Sept. 7, during a town hall event hosted by MSNBC, Republican presidential candidate Donald Trump stated he would have “a good relationship” with Russian president Vladimir Putin. It wasn’t the first time he made that claim. (Adriana Usero/The Washington Post)

The candidates appeared sequentially, not face to face, at the USS Intrepid museum in New York before an audience of military service members and veterans. The old aircraft carrier, commissioned during World War II and retired after Vietnam, was an apt setting for hearing the candidates’ positions on foreign and defense policy. But only one of them had anything meaningful to say.

Hillary Clinton went first and was immediately hit with a barrage of questions about her emails. Some commentators said afterward that she sounded defensive, but that line of criticism is absurd. How is one supposed to sound when pressed to defend oneself? Have we finally reached the point when a woman is allowed to speak forcefully on her own behalf? Or do we still expect, at all times, a demure smile?

As would be anticipated from a former senator and secretary of state, Clinton displayed her knowledge and experience. The headline, I suppose, would be this pledge: “We are not putting ground troops into Iraq ever again. And we’re not putting ground troops into Syria.” Those who worry she might prove too hawkish as president may feel relieved.

But the evening was really about Trump, and the stakes are far too high for him to be graded on a curve. No, he did not rant and rave like a crazy man or threaten to nuke anybody. But neither did he give the slightest indication he knew anything about the issues he was supposed to be talking about. Read the transcript and try to find one sensible and substantive thing he had to say.

On top of insisting that Putin is a great guy, Trump denigrated the U.S. military’s high command. “I think under the leadership of Barack Obama and Hillary Clinton, the generals have been reduced to rubble,” he said. “They have been reduced to a point where it’s embarrassing for our country.”

Lauer recalled that Trump has long claimed to have a secret plan for defeating the Islamic State, but now says he would ask “the generals” to submit a plan within 30 days for victory over the terrorist group. Reminded that he has boasted that he knows more about the Islamic State than our military leaders do, yet now says he wants them to come up with a plan, Trump replied: “Well, they’ll probably be different generals, to be honest with you.”

In other words, he promises a purge at the Pentagon. Maybe his friend Vladimir can give him pointers.

Democratic presidential nominee Hillary Clinton and her Republican opponent Donald Trump answered questions on national security and foreign policy Sept. 7 during a “commander-in-chief forum” on NBC News. (Video: NBC News/Photos: Melina Mara/Post, Mike Segar/Reuters)

And there’s more: Trump repeated his complaint that the United States should have “taken the oil” in Iraq, noting that “it used to be, to the victor belong the spoils.”

Yes, that was true in the time of Genghis Khan. Today, under international law, plunder is a war crime — and not the only one Trump wants our military to commit. He has said in the past that our forces also should practice torture “worse than waterboarding” against suspected terrorists. He would ask our service members to dishonor the uniform and all it represents.

Trump defended a 2013 tweet about the problem of sexual assault in the military in which he asked, “What did these geniuses expect when they put men & women together?” He said the solution was to “set up a court system within the military.” Unbelievable.

Face the truth: Trump has to be the most dangerously ignorant major-party presidential candidate in history.

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