Joe Biden is now officially the 46th president of the United States — and with it, the fourth commander in chief to inherit the war in Afghanistan, America’s longest conflict since the Republic’s founding 245 years ago. Biden will immediately confront the same question Donald Trump faced in his first several weeks on the job: What is the best way to extricate U.S. forces from a civil war that doesn’t have a U.S.-made solution?

Afghanistan is experiencing a turbulent time in its history, with meandering peace talks coexisting alongside bloody violence. But after taking a more strategic view of U.S. interests, the Biden administration’s best course of action is to continue the current U.S. troop drawdown in Afghanistan. There is nothing left in Afghanistan for the U.S. to win.

Big picture, Biden will be presented with three general Afghanistan policy options: 1) maintain a U.S. counterterrorism presence for the foreseeable future, 2) enter into new negotiations with the Taliban in order to extend Washington’s stay and give intra-Afghan diplomacy more time, and 3) continue implementing the February 2020 U.S.-Taliban agreement until all U.S. troops are out of Afghanistan by May 1.

The first option is a popular one in Washington, for it provides a sense of comfort that transnational terrorist groups like al-Qaida and Islamic State-Khorasan will remain vulnerable to U.S. military pressure. Biden appears amenable to this view, telling Stars and Stripes last September that he would prefer a 1.500-2,000 U.S. troop contingent in Afghanistan with a strict counterterrorism function. Antony Blinken, Biden’s secretary of state-designate, hinted at the likelihood of a similar residual troop presence during his Tuesday confirmation hearing.

However, a long-term counterterrorism deployment is not as easy as its proponents think. There are costs to keeping a residual U.S. troop presence in Afghanistan that go beyond additional casualties and expense (the U.S. has already spent close to $2 trillion on the war over the last 20 years). The most immediate is the risk of mission creep, where an otherwise narrow mission morphs into a more expansive one over time. This wouldn’t be a new experience for the U.S. in Afghanistan. In the opening months of the war, Washington saw its original mission of eradicating al-Qaida and punishing the Taliban transform into a state-building exercise. Defending the homeland was replaced with building, defending and stabilizing a corrupt country in the heart of South Asia — a hubristic objective that was out of the U.S. military’s capacity. While one can hope U.S. officials have learned from past experience, it would be unwise to rationalize Afghanistan policy on that assumption.

The second option is also fraught with problems. First, there is no evidence the Taliban would be interested in a renegotiation. The Taliban control more of Afghanistan’s territory today than at any point since early 2001. The facts on the ground remain favorable to the Taliban, who have escalated operations against the beleaguered Afghan security forces to enhance leverage at the negotiating table. The Taliban simply have no incentive to cooperate on any renegotiation. Issuing an ultimatum to the Taliban is highly unlikely to change their behavior either. This is a movement that has resisted a superpower for two decades.

The U.S. could theoretically take action itself, for example by reneging on the May 1 withdrawal date. Unfortunately, Taliban leadership would interpret such a move as a unilateral violation, in which case hostilities between Taliban fighters and U.S. troops could very well resume to their previous levels. The insurgency has largely held their fire against U.S. troops over the last year due to the Doha withdrawal deal; renege on that deal, and the physical risk goes up for the U.S. troops forced to stay in country.

Some contend that tying further troop reductions to the intra-Afghan peace process is prudent. But this would merely delay a U.S. withdrawal for months, if not years. It would also provide Afghan President Ashraf Ghani, already resistant to conceding on anything that would threaten his presidency, with a reason to slow things down or walk away from the diplomatic process entirely.

This leaves one policy option for the Biden administration: continue to execute the withdrawal ushered in by Trump. In addition to being a decision the vast majority of the American public would support (the group Concerned Veterans for America found that two-thirds of U.S. veterans support withdrawing all troops from Afghanistan), a full withdrawal would more importantly cut the cord on the longest war in America’s history. And with Washington no longer at the center of the civil war, Afghanistan’s neighbors would be forced to take full ownership of the conflict — a conflict that affects their security far more than it affects the security of the U.S.

There are those in the U.S. foreign policy community who believe leaving Afghanistan behind will automatically result in the next 9/11. But given Washington’s global strike capability, a $60 billion intelligence budget and a U.S. counterterrorism apparatus that is second-to-none, this contention should be viewed as nothing more than the last-ditch defense of a failed status quo.

If Joe Biden wants to reorient U.S. foreign policy in a better direction, he can begin by formally ending the longest war in U.S. history. U.S. troops have done what they’ve been ordered to do since the first days of the conflict 20 years ago. Biden should now order them home.

Daniel R. DePetris is a fellow at Defense Priorities and a columnist at Newsweek.

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