Afghanistan nagged at Joe Biden 10 years ago. He thought the Pentagon was muscling a new president, Barack Obama, into adding more troops for an unwinnable war. He believed the United States’ interests in Afghanistan should be focused on preventing another attack against the homeland.

This week, as president himself, Biden decisively reversed the choices made a decade ago and decided to withdraw all troops by Sept. 11, the 20th anniversary of the ghastly al-Qaeda attacks that skewed U.S. foreign policy for two decades. It’s a gutsy move because the price of being wrong is enormous.

Military advisers, now as a decade ago, have been warning Biden of the dangers. Intelligence analysts predict that civil war may quickly erupt, and the Kabul government may collapse. They predict that al-Qaeda and other terrorist groups could reestablish havens within two years. They fear that Islamist militants around the world, who have been on the defensive since the defeat of the Islamic State, will be emboldened by what the Taliban will claim as a victory.

Many military leaders have been urging that Biden announce a conditions-based withdrawal. Biden, in the end, rejected that course, deciding that linking withdrawal to conditions on the ground, in the words of a senior administration official who briefed reporters today, “is a recipe for staying in Afghanistan forever.”

Biden sometimes comes across as a genial gaffer, pliable in the way of a career politician. But Tuesday’s announcement shows that he is also a stubborn and resolute man. Friends say he was bruised by the Afghanistan battles of a decade ago and took away some grudges. When convinced he’s right, he’s prepared to take big risks — as he has this week.

The military, for all its worries about withdrawal, has hated the meat grinder of Afghanistan. Most of today’s Army and Marine commanders have fought there, and many of their sons and daughters have, too. They share Biden’s desire to get the hell out. But that’s checked by a feeling that the only thing that’s worse than remaining in what seems an unwinnable stalemate is pulling out troops — and then having to go back in.

That’s what happened in Iraq after the withdrawal of U.S. forces in 2011. They were back five years later, dealing with the slaughterhouse that was the Islamic State. And if Biden was right about Afghanistan 10 years ago, he was dead wrong about getting out of Iraq, which he also strongly advocated.

That’s the awful danger of this decision. Sometimes cutting the knot and removing U.S. troops opens the way for peace; more often, in recent years, it has been a prelude to greater bloodshed.

The downside is easy to imagine: a spiral of violence in which provincial capitals fall, one by one, leading to a deadly battle for Kabul — a fight in which the people who believed most in the United States’ intervention will be at greatest risk, and pleading for help. Closing our eyes and ears to that catastrophic situation — turning away from the desperate appeals, especially from the women of Afghanistan, who fear new oppression — will require cold hearts and strong stomachs.

Biden decided this week that Afghanistan’s fate, in the end, will be determined by its people. Those who suspect that the country will quickly tumble back into the Middle Ages and a primitive version of Islam are wrong, I suspect. The years of war have modernized Afghanistan. It’s now a richer, more urban country, connected by modern communications. People who gained their freedom in the two decades under a U.S. umbrella won’t give it up easily.

The real test of Biden’s policy is whether the core national interest he has embraced — of limiting U.S. involvement in Afghanistan to preventing another 9/11-type attack on the homeland — can be achieved without U.S. troops on the ground.

Officials have been arguing this question back and forth for weeks. Can the CIA maintain a clandestine force in Afghanistan that’s strong enough to operate against al-Qaeda and other terrorist groups? Will drones be effective, if they must now be based in the Persian Gulf, with long flight times to Afghanistan and much shorter periods over potential target areas? We don’t know the answers. Biden is rolling the dice.

Presidents have a few moments in office where they must make gut decisions about the nation’s security. Because the future is unknowable, a commander in chief must trust his instincts. Fred Charles Iklé titled a book about ending the quagmire of Vietnam, “Every War Must End.” Now that Biden has made his choice, he must pray that the troops he is bringing home will never have to go back.

Read more: