In the beginning, it all looked like a brilliant military victory and a validation of Defense Secretary Donald Rumsfeld’s new way of fighting and winning modern wars.

Less that a month after the Sept. 11 attacks that galvanized the nation’s resolve and launched what would eventually be called the Global War on Terror, Rumsfeld stood behind the lectern of the Pentagon briefing room, flanked by Joint Chiefs Chairman Gen. Richard Myers, and announced the beginning of combat operations.

It was the afternoon Sunday, Oct. 7, 2001, and Rumsfeld outlined the objective of the initial strikes against the Taliban and the al Qaeda terrorists they were harboring.

“The campaign against terrorism will be broad, sustained, and that we will use every element of American influence and power,” Rumsfeld vowed. The plan was to “take the battle to the terrorists” who had killed thousands of Americans and who threatened not just the United States but the entire world.

The conventional wisdom about warfighting at the time was known as the “Powell Doctrine,” named for former Joint Chiefs Chairman Gen. Colin Powell, who advocated the use of “decisive force” to overwhelm any enemy and ensure a quick victory.

But Rumsfeld had other ideas, and he pressed his commanders to use a small number, roughly 1,000, of American special operations troops and CIA paramilitary forces to ally with the Taliban’s historic enemies, while providing the indigenous forces with pinpoint airstrikes to quickly crush the Taliban.

“Territory began to fall to our Afghan allies more quickly that we had imagined possible,” Rumsfeld wrote in his 2011 memoir Known and Unknown. “By early December, two months to the day since the start of our combat operations, the Taliban had been pushed out of every major city in Afghanistan,” he recalled.

Flush with success, Rumsfeld scoffed when the New York Times questioned whether Afghanistan might become another Vietnam, “another stalemate on the other side of the world,”

“Like an unwelcome specter from an unhappy past, the ominous word ‘quagmire’ has begun to haunt conversations among government officials and students of foreign policy, both here and abroad,” the paper said in a front page story just three weeks into the war.

But with advantage of hindsight, over the years Rumsfeld’s "light footprint" strategy has faced criticism from military analysts who argue his refusal to raise U.S. troop levels allowed Osama bin Laden to initially escape and for the Taliban eventually to stage comeback.

“When they went back on the offensive [in 2006], they found little to stand in their way,” wrote historian Max Boot, in a review of Rumsfeld’s memoir.

The administrations of both Presidents George W. Bush and Barack Obama have tried to extract the U.S. from Afghanistan by building up the Afghan military, which numbered around 36,000 in 2006, to around 300,000 today, while drawing down U.S. forces.

Last year, President Trump, who wanted to call it quits in Afghanistan, was convinced by his advisers that an abrupt departure would dishonor the memory of U.S. troops who have died there and leave behind a failed state that would once again be a breeding ground for terrorists.

“A hasty withdrawal would create a vacuum for terrorists, including ISIS and Al Qaida, would instantly fill just as happened before September 11th,” Trump said in an August 2017 speech in which he announced a new policy to increase the number of U.S. military advisers and unleash airstrikes to pound the Taliban in an effort to break their will and drive them to make a peace deal.

This past week, the top U.S. commander for the region insisted that despite what he called “a difficult and bloody summer” and the lack of any measurable gains on the battlefield, the Trump policy is succeeding.

“This strategy is sound and it is working, whereas the Taliban's strategy of waiting us out is an untenable one,” Gen. Joseph Votel, the head of the U.S. Central Command, told reporters at the Pentagon Thursday.

“The taste for peace and reconciliation remains strong following this summer's cease-fire, and we continue to see local reconciliation initiatives around the country,” Votel said, while conceding, “a challenging fight remains as we work with regional and international partners to apply the military pressure to the Taliban that will convince them that reconciliation is the only way forward.”

But as the conflict enters its 18th year on Sunday, it still remains a stalemate.

“If the U.S. has any real strategy in Afghanistan, it seems to be fighting a war of attrition long enough and well enough for the threat to drop to a level that Afghan forces can handle or accept a peace settlement credible enough for the U.S. to leave,” wrote Anthony Cordesman in a recent analysis for the Center for Strategic and International Studies.

“Even with direct costs that now seem likely to exceed one trillion dollars, more than 2,200 dead, and more than 20,000 wounded in action, the U.S. commitment is as open ended as ever,” Cordesman wrote. “This is a literal triumph of hope over experience.”

The lesson of Afghanistan may be that the best chance to avoid a prolonged, grinding insurgency may be at the beginning of the conflict, argues Stephen Biddle, a professor of International and Public Affairs at Columbia University.

“If the U.S. had offered power sharing to the Taliban back in 2002, when we were strong and they were weak, we probably would've gotten a better deal than we're going to get now, 17 years later,” he said.

The other takeaway, Biddle says, is that counterinsurgency is not impossible, but it is expensive and it takes a very long time to succeed unless you get lucky. “If you're not willing to make the full investment, then half measures will usually get you a lot less than half a loaf."