WASHINGTON — President Biden’s decision to pull all American troops from Afghanistan by Sept. 11 was rooted in his belief that there is no room for continuing 20 years of failed efforts to remake that country, especially at a moment when he wants the United States focused on a transformational economic and social agenda at home and other fast-evolving threats from abroad.

Though Mr. Biden would never use the term, getting out of Afghanistan is part of his own version of “America First,” one that differs drastically from how his predecessor, Donald J. Trump, used the phrase. His years on the Senate Foreign Relations Committee and as vice president convinced him that the United States-led effort in Afghanistan was destined to collapse of its own weight.

Time and again during the Obama administration, Mr. Biden lost arguments to reduce the American presence to a minimal counterterrorism force. But after less than three months as president, Mr. Biden came to the determination that only a full withdrawal — with no link to political conditions on the ground — would wrench America’s attention away from the conflict of the past two decades in favor of the very different kinds he expects in the next two.

He has defined his presidency’s goals as releasing the country from the grip of a virus that is morphing into new variants, seizing an opportunity to bolster economic competitiveness against China and proving to the world that American democracy can still rise to great challenges.

And in that vision, the priorities are fighting poverty and racial inequities and increasing investment in broadband, semiconductors, artificial intelligence and 5G communications — not using the military to prop up the government of President Ashraf Ghani. It means thinking about infrastructure instead of force protection, and defending commercial supply chains instead of military supply lines.

Mr. Biden’s approach carries clear risks. The annual worldwide threat assessment published by his intelligence chiefs on Tuesday morning, as word of his decision leaked, explicitly warned that “the Afghan government will struggle to hold the Taliban at bay” if the American-led coalition withdraws. Administration officials said that raised the specter of something akin to the 1975 fall of Saigon, after the United States gave up on another ill-considered war.

But Mr. Biden’s decision makes clear his belief that contending with a rising China takes precedence over the idea that with just a few more years in Afghanistan, and a few more billions of dollars, the United States could achieve with a few thousand troops what it could not achieve with hundreds of thousands and the more than $2 trillion already poured into two decades of warfighting and nation building.

After Mr. Biden declared at a news conference last month that “We’ve got to prove democracy works,” he went on to describe a foreign policy that was focused on restoring America’s reputation for getting big things done. “China is outinvesting us by a long shot,” the president noted, “because their plan is to own that future.”

Indeed, no one celebrated the American involvement in Afghanistan, or Iraq, more than the Chinese — conflicts that kept Americans up at night worrying about casualties and taking control of distant provinces, while Beijing focused on spreading its influence in regions of the world where America was once the unquestioned dominant power.

Several years ago, at China’s Central Party School, a recently retired Chinese military officer said his colleagues marveled at how the United States was wasting its assets.

On Tuesday, one of Mr. Biden’s top advisers suggested that the president had come to the same conclusion. To address the threats and challenges of 2021 rather than those of 2001, he said, “requires us to close the book on a 20-year conflict in Afghanistan.”

But that choice comes with considerable risks, which is why it took two and a half months, and some contentious arguments with the Pentagon leadership, to make it.

His advisers acknowledged that the president would take the blame if Afghanistan collapsed into the hands of the Taliban, or, of much greater concern, again became a haven for terrorists intent on striking the United States.

Mr. Biden’s critics wasted no time painting the decision as a sign of the United States in retreat, ignoring that only six months ago, Mr. Trump declared, erroneously it turned out, that he would have all American troops home for Christmas.

Senator Lindsey Graham, Republican of South Carolina, who also tried to persuade Mr. Trump to stay, called the decision “dumber than dirt and devilishly dangerous.”

And while Democrats were generally supportive, some expressed concern about maintaining the ability to deal militarily with the emergence of a threat from Afghanistan.

“There’s no easy answer,” said Senator Jack Reed, Democrat of Rhode Island and an influential voice on the Armed Services Committee. The key, he said, would be “a very determined counterterrorism operation.”

But as Lisa Curtis, the senior director for South and Central Asia on the National Security Council under Mr. Trump, put it, the hard question was where to locate those forces — and how to get them back into hostile territory when needed.

“Getting them back into Afghanistan to deal with terror groups becomes increasingly difficult as the Taliban takes over greater and greater portions of the country,” said Ms. Curtis, now at the Center for a New American Security.

“It shouldn’t be an either-or,” she added. “We should be able to sustain a certain level of forces in Afghanistan, because we can deal with more than one threat at a time.’’

That was not the view of her boss, Mr. Trump, who wanted to exit Afghanistan but never laid out a plan.

When historians look back at this moment, they may conclude Mr. Biden’s decision was predestined.

The place is not called the Graveyard of Empires for nothing: The British pulled out in 1842, after an expedition their textbooks call the “disaster in Afghanistan,” and the Soviets in 1989, after a decade of death and frustration. What Soviet leaders learned in a decade, four American presidents learned over the span of two.

Mr. Biden was an early convert to the idea of heading to the exits, though he lost the argument in 2009, during President Barack Obama’s first policy review. In his memoir, Mr. Obama recalled his vice president warning him at the time about an “unrestrained” American military that was dragging “the country deeper into a futile, wildly expensive nation-building exercise.”

Mr. Biden still believes that, but now he has gone one step further by rejecting the Pentagon’s insistence that any withdrawal be “conditions-based” — in other words, reversible if it looks as if the Afghan government is at risk of losing control.

In short, Mr. Biden is declaring that war is over — no matter what, and even though the United States is leaving with most of its goals unmet, and Afghanistan’s stability deeply in jeopardy. If there is no terrorist attack launched from Afghan territory again, no echo of Sep. 11, 2001, Mr. Biden may well have been judged to have made the right bet.

In the end, the argument that won the day is that the future of Kenosha is more important than defending Kabul. And if Mr. Biden can truly focus the country on far bigger strategic challenges — in space and cyberspace, against declining powers like Russia and rising ones like China — he will have finally moved the country out of its post-9/11 fixation, where counterterrorism overrode every other foreign policy and domestic imperative.

That would be a real change in the way Americans think about the purpose of the country’s influence and power, and the nature of national security.