Democrats’ Afghan Strategy Sounds Familiar. It’s a Lot Like Trump’s.

For 18 years and four presidential elections, Democrats running for president have felt compelled to lay out comprehensive plans for the future of Afghanistan, vowing to never again let the country become a breeding ground for terrorists who could strike the United States as they did on Sept. 11, 2001.

Now, the candidates are racing one another — and President Trump — to demonstrate how quickly they would end the long-running conflict. In the debate on Thursday night, there was almost no discussion of American goals for the country, like building a democracy or protecting the rights of women — objectives that were staples of past Democratic campaigns.

It is a striking change. Even while deeply opposing President George W. Bush’s war in Iraq, Democrats saw Afghanistan as the good war, prompted by a direct attack on the United States. President Barack Obama ordered a surge in American forces by the end of his first year in office. But as the years went by, he had growing doubts, and now Democrats have fully embraced those misgivings and want out.

Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont and former Vice President Joseph R. Biden Jr. are so eager for the United States to depart that they say they would pull out combat troops even in the absence of an agreement with the Taliban.

“What we’re doing right now in Afghanistan is not helping the safety and security of the United States,” Ms. Warren said during the debate. “It is not helping the safety and security of the world. It is not helping the safety and security of Afghanistan.”

“We cannot ask our military to keep solving problems that cannot be solved militarily,” she added.

A foreign policy adviser to Mr. Sanders, who has said he would withdraw all American troops from Afghanistan in his first term as president, echoed that argument in an interview on Friday, saying that while Mr. Sanders supported negotiations with the Taliban, the next president should be “modest about what we, the United States, can actually achieve given that we’ve been there for almost two decades.”

Pete Buttigieg, the mayor of South Bend, Ind., and the only candidate to have served in Afghanistan, acknowledged during an interview over the weekend that what the Democrats missed last week was any discussion of what the United States still wanted or needed to achieve in Afghanistan — the first step toward determining what kind of presence to have on the ground.

“I will say I agree that didn’t come through in the debate,” said Mr. Buttigieg, who has pledged to withdraw the troops within a year of taking office, but only with a substantive peace deal with the Taliban. “It almost came across as if the candidates think there is no point to being there, which is not how I view it.”

Mr. Buttigieg said that could be a reflection of wariness over “endless war,” and the confusion generated by a conflict in which the American goals have often seemed to shift. He recalled that when he exercised at the gym at the headquarters of the international security force in Kabul, he would stare at a large graphic that had “eight lines of effort on it, and it was very hard to understand what the scope of the mission was.”

Yet even the central goal of protecting the American homeland from another attack, a staple of John Kerry’s run for the presidency in 2004 and Mr. Obama’s in 2008, barely gets a mention now. Mr. Kerry told The New York Times in 2004 that any effective Afghanistan plan “requires destroying terrorists. And I’m committed to doing that. But I think I have a better way of doing it.”

Five years later, Mr. Obama overruled warnings from his ambassador in Kabul that his administration’s plan to surge troops into the country, then depend on the Afghan government to defend itself, would probably not work. Speaking at West Point, Mr. Obama said he had “determined that it is in our vital national interest to send an additional 30,000 U.S. troops to Afghanistan. After 18 months, our troops will begin to come home.” Quietly, his White House set up an “Afghan Good Enough” committee to find an exit.

The current presidential candidates seem uninterested in revisiting those decisions. Instead, they race to reassure voters about how quickly they would bring the remaining 14,000 troops home.

To some Democrats who devoted years to stabilizing Afghanistan, the candidates are losing an opportunity to take on Mr. Trump for what they view as a feckless foreign policy, one in which the president is trying to rush through a bare-bones peace agreement with the Taliban so that he can announce major troop withdrawals before the 2020 election.

“It would be unworthy of the U.S. to leave the Afghan people and government to the mercies of the Taliban in an unequal agreement,” R. Nicholas Burns, a former under secretary of state for policy and now an adviser to Mr. Biden, said over the weekend.

As ambassador to NATO in the early years of the war, Mr. Burns took allies to Afghanistan to persuade them to join the coalition, declaring that it was in their own interest to stabilize the country, where 2,400 Americans have died in combat, along with 1,000 troops from NATO and other nations. “Trump has displayed astonishingly weak negotiating skills by signaling to the Taliban his desperation to withdraw American forces ahead of the 2020 election,” he said.

But if the Taliban were tuned into the recent debates, or were reviewing the positions the candidates have posted on their websites, they would most likely conclude that no matter who gets elected, they are on the verge of achieving their central goal: getting American forces out of the country.

Mr. Biden himself, a voice for more rapid withdrawal during the Obama administration, now advocates keeping an intelligence presence — though in the debate he said it would be across the border in Pakistan.

“We can prevent the United States from being the victim of terror coming out of Afghanistan by providing for bases — insist the Pakistanis provide bases for us to airlift from and to move against what we know,” Mr. Biden said after one of the moderators quoted Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, saying that Afghanistan still needed military support to prevent violence. “We don’t need those troops there. I would bring them home.”

Mr. Biden’s longtime national security adviser, Antony Blinken, refined that on Sunday, saying the candidate would “draw down our combat forces and narrowly focus the mission on counterterrorism, with small numbers of special operators and intelligence assets in and around Afghanistan. He would rally the world to support Afghans’ human rights and continued development efforts.”

Senator Kamala Harris of California said in an interview with The Times this year that while she supported withdrawing troops, she believed the United States needed some sort of continued presence in Afghanistan to support the government and stop terrorists from regrouping.

“The question is the type of presence,” she said. “I think that it is completely appropriate that we would give support to the Afghan government in terms of helping them train their troops and thinking about how we can provide assistance so that they can have their own people up and running in a way that they keep their country secure, and in particular prevent it from becoming a haven” for terrorists.

One of the curious elements of the presidential campaign is that Afghanistan has been the only foreign policy issue actively debated among Democrats. There has been little to no debate about the far bigger strategic questions raised by the revival of superpower tensions with Russia and China. The growing confrontation with Iran and the president’s dealings with Kim Jong-un of North Korea have barely been mentioned.

Perhaps that is because the Afghan conundrum is so familiar to voters, and goes to a central question: When would these aspirants for the Oval Office use traditional military force?

Mr. Buttigieg — noting that Congress’s 2001 Authorization for Use of Military Force has allowed the war in Afghanistan to continue for so long that, very soon, the soldiers fighting it will include people who were not born when the law was passed — said that as president, he would put a three-year limit on such authorizations and require a congressional vote to renew them for longer.

“If there’s one thing we’ve learned from Afghanistan,” he said, “it’s that the best way not to be caught up in endless war is to avoid starting one in the first place.”

None of the candidates seem particularly impressed by the argument that withdrawing troops would create a vacuum in Afghanistan for the Taliban and other terrorist groups to fill.

“It’s a false choice to say we need an enduring combat presence in Afghanistan or we open ourselves to an unmanageable terrorist threat,” a spokeswoman for Ms. Warren said. “International terrorism is a worldwide challenge, and it is best confronted not with boots on the ground in Afghanistan, but instead with diplomacy and intelligence and through coordination with partners and allies.”

Mr. Sanders would continue the United States’ intelligence presence in Afghanistan, according to his campaign, but focus on humanitarian and developmental incentives, not military pressure, to bring the Taliban to the table and reach a peace deal. He and Ms. Warren made very similar arguments.

“I was in Afghanistan with John McCain two years ago this past summer,” Ms. Warren said at the debate. “We talked to people on the ground and asked the question, the same one I ask on the Senate Armed Services Committee every time one of the generals comes through: ‘Show me what winning looks like. Tell me what it looks like.’ And what you hear is a lot of ‘Uh,’ because no one can describe it. And the reason no one can describe it is because the problems in Afghanistan are not problems that can be solved by a military.”