Iran could have been helpful; Trump has rebuffed it in his Saudi love trance. Russia could have been helpful; Trump is paralyzed by his Moscow secrets with respect to President Vladimir V. Putin. So Iran and Russia will do their worst in Afghanistan. As for China, another important regional player, it did not even get a mention.

Trump invited India “to help us more with Afghanistan” — effectively holding a red rag to the Pakistani bull. The military in Pakistan will be enraged by the combination of Trump’s blunt (if justified) criticism and blandishments to India. This looks like sheer diplomatic stupidity. I wonder if the State Department, whose expertise has been flouted since January, even got to vet the speech.

The Afghan war could have been ended a long time ago when people still remembered what it was about. But the United States diverted its forces and treasure to Iraq. Then Obama, in preparing to withdraw from Iraq, tried to compensate with a hapless “surge” in Afghanistan. This is a zigzagging chapter in American military history that soldiers are not about to resolve now. The mission became a mess; some 2,400 American troops have given their lives for a moving target. Trump’s words did nothing to redress this shame.

“Trump put forward no coherent plan for finishing the war,” Vali Nasr, the dean of the Johns Hopkins School of Advanced International Studies, told me. “He needs a serious diplomatic tack.”

The problem is Trump has no notion of diplomacy. He looked like an impersonator as he spoke, a man pretending to be something we know he’s not. A man of such evident moral shallowness, to whom personal sacrifice is a stranger, cannot speak of valor, bravery and heroism without becoming cringe-worthy.

He spoke of “principled realism.” His presidency has been about unprincipled recklessness: allies shunned, dalliances with dictators, environmental sabotage. The man who earlier this month could not distinguish between neo-Nazi white supremacists with blood on their hands and leftist protesters calls for America’s soldiers to come home to a country that rejects bigotry and “has renewed the sacred bonds of love and loyalty.”

Really?

Shortly after Kelly, Trump’s chief of staff, lost his son in Afghanistan, he gave a eulogy for two marines killed in Iraq. Kelly described how, confronted by a suicide bomber in a truck, “they never stepped back. They never even started to step aside. They never even shifted their weight.”

For that brave act, of course, they needed something Trump will never have: a center of gravity.