The engineers left the helicopter first, hauling explosives. One of them would be dead by noon.

The war has again found its way back into the political discourse. President Trump invited the Taliban to Camp David, then canceled the invitation after an attack that killed an American soldier. The peace talks are off, but the pressure to bring American troops home seems to be building, even without a deal. Mr. Trump and his aides, and the Democratic presidential candidates, seem to be saying that the war was only about routing Al Qaeda after the Sept. 11 attacks, though Al Qaeda was protected then by the Taliban, who have been fighting us on the ground ever since.

[An American Special Forces soldier was killed in eastern Afghanistan on Monday. The soldier is the 17th American service member to die during combat operations this year.]

Those first few hours in Marja, we felt like we’d won some sort of lottery, like we’d get our shot at a version of Falluja, the brutal Marine battle in Iraq, or Hue in Vietnam. We’d invade the city, raise the flag and install a local government. “Pages of history,” our battalion commander said.

But Marja wasn’t really a city. It was a bunch of hamlets within opium-poppy fields atop an American agricultural project from decades before, a failure of previous national security thinking. And now it was the high-water mark of the American military’s acceptance of counterinsurgency, the doctrine of trying to win over the locals by clearing away militants, building schools, laying roads. We were fighting the Taliban to let Afghanistan build a democracy. Or something like that. That’s how they presented it to us as they sent us in.