Secretary of Defense Jim Mattis announced on September 18 that the US will send more than 3,000 troops to Afghanistan in an effort to win America’s 16-year war there — the longest in US history. It’s also a reversal for President Trump, who entered office promising to minimize America’s involvement abroad.

They will add to the approximately 11,000 US troops already serving in Afghanistan, bringing the total to at least 14,000. These new service members will help Afghan forces in their effort to defeat the nearly 20 terrorist groups in the country — especially the Taliban, ISIS, and al-Qaeda — by advising them and providing artillery and air support.

The announcement comes less than a month after Trump outlined his war strategy in a high-profile August 21 speech in front of around 2,000 troops at Fort Myer, Virginia. Trump said the US would win the war but didn’t disclose when US troops would come home. “Conditions on the ground, not arbitrary timetables, will guide our strategy from now on,” he said in his remarks, which were heavy on harsh rhetoric but strikingly light on details.

One day after Trump’s comments, Secretary of State Rex Tillerson offered a different assessment of America’s goals in Afghanistan. “I think the president was clear this entire effort was intended to put pressure on the Taliban, to have the Taliban understand that you will not win a battlefield victory,” Tillerson said during a press conference on August 22. “We may not win one, but neither will you.”

As Tillerson hinted, it’s unclear how sending a few thousand more troops will turn around the dire situation in Afghanistan. In 2011, the US had around 100,000 troops deployed in the country. Yet the Taliban — the hardline Islamist group that America and NATO set out to dislodge more than 15 years ago — survived and has recently made a startling comeback. It currently controls more than 40 percent of the country, and around 8.4 million Afghans, about a third of the country’s population, live under its rule.

But by deploying these troops, Trump becomes the third president — joining George W. Bush and Barack Obama — to wade into the quagmire. It’s a stunning turnaround for Trump, who spent years railing against leaders who waded into unwinnable conflicts.

Trump goes against his “instinct”

Trump was inherently skeptical about spending more blood and treasure in Afghanistan, and tweeted for years about how much he didn’t like the war:

When will we stop wasting our money on rebuilding Afghanistan? We must rebuild our country first. — Donald J. Trump (@realDonaldTrump) October 7, 2011

Trump’s isolationist views form the core of his “America First” foreign policy. “The world must know that we do not go abroad in search of enemies,” reads the foreign policy section of the White House website.

And during a months-long Afghanistan strategy review led by National Security Adviser H.R. McMaster, Trump questioned why the US was doing so poorly in South Asia after spending around $714 billion and losing a total of 2,264 troops and civilians — with little to show for it.

He even threatened to replace Gen. John Nicholson, the top commander in Afghanistan, who warned Congress in February that the conflict was at a “stalemate” and required thousands more US troops in the region to break it.

But in his August speech, Trump admitted that he put those concerns aside and went against his beliefs. “My original instinct was to pull out — and, historically, I like following my instincts,” he said, adding that he changed his mind partly because of the many terrorist groups in Afghanistan. Breitbart reported that Trump’s base was unhappy with his “flip flop.”

How well the US fares in Afghanistan now will be part of the America First president’s legacy. That puts a lot of pressure on the few thousand American sons and daughters headed into harm’s way.