I had come to learn (as the president had already to his great dismay) that the legal and policy morass that had developed around Guantanamo meant it could not simply be “closed.” A task that many saw as a matter of decisively turning the page on a dark chapter in American history turned out to be much messier, more tedious and more legally and politically fraught than I anticipated. It was a hard enough diplomatic challenge to convince foreign partners to agree to take in former Guantanamo detainees. At home, the hyper-polarized political environment and myriad legal obstacles made the process even harder. The detention facility and surrounding legal infrastructure had been thrown together hastily in the shadow of a horrific national trauma, with little attention to future legal repercussions, including the likelihood of winning criminal convictions. In large part, the Guantanamo mess is self-inflicted — a result of our own decisions to engage in torture, hold detainees indefinitely without charge, set up dysfunctional military commissions and attempt to avoid oversight by the federal courts.

Now we stand 20 years from the opening of Guantanamo on Jan. 11, 2002. The United States has left Afghanistan, and the 20th anniversary of the 9/11 attacks has come and gone. The alleged perpetrators still have not been tried, and numerous other men remain held in indefinite detention without charge. President Joe Biden is completing his first year in office. My State Department office remains empty. Our longest war has ended, yet Guantanamo endures.

The challenges presented by closing Guantanamo have not changed — but nearly everything else has. The world has moved on from the 9/11 era; even more than during the Obama years, Guantanamo feels today like a relic of another time. Biden, who will be remembered as the president who ended a war that three of his predecessors could or would not, should recommit to closing the facility for good. This may require bolder solutions than his predecessor and some imperfect compromises — including finally abandoning the experiment with military trials — as well as the same resolve and leadership Biden demonstrated in extricating the United States from Afghanistan. The time has come to finish the yearslong process of restoring U.S. moral credibility by untangling the knots that we ourselves tied in Guantanamo.

By the time I took the job in July 2015, we knew it would be hard for Obama to fulfill his campaign promise of closing the notorious detention facility in Cuba. A principal reason was a law passed by Congress during his first term that purported to prevent the president (in my view, probably unconstitutionally) from transferring any Guantanamo detainees to the United States for any purpose. Before that, it was taken as a given that although we would resettle as many prisoners as possible abroad, a handful of those awaiting military commission trials — such as the 9/11 and USS Cole co-conspirators — would have to remain in U.S. custody, ideally at a secure location other than Guantanamo.

But Congress’ transfer ban effectively trapped those detainees in Cuba, preventing Obama from closing Guantanamo (without taking unilateral action for which some believed he lacked the legal authority). So we focused intensely and unremittingly on getting as many people as we could out before the end of Obama’s presidency, even if the facility itself would not be closed at that time.

For a detainee to be able to leave Guantanamo, the first step was a careful whole-of-government review to determine whether that individual’s continued detention was necessary to counter an ongoing, significant threat to the United States. If all six agencies and departments involved in the review unanimously concluded that it was not, the detainee became “approved for transfer.” Then, it was my job to negotiate his repatriation to his country of origin or resettlement to a third country, along with security arrangements and diplomatic assurances intended to maximize the chances for successful reintegration to life outside Guantanamo.

The negotiations were difficult, but I welcomed the task because, unlike in other areas of diplomacy, success or failure could be easily and quantifiably measured. Given the way my position was set up, I was able to wield the considerable, full leverage of U.S. diplomacy and find hidden opportunities. Countries agreed to take detainees for a number of reasons. Some foreign leaders thought the facility was an abomination and simply wanted to help us close it. Some partners were reluctant to even entertain the notion despite having benefited disproportionately from the enormous investment of American blood and treasure since 9/11 to keep us — and them — safe. I told them, sometimes repeatedly, that we were all obligated to help where we could, including with winding down Guantanamo.

Others wanted entirely unrelated concessions in exchange for a commitment to resettle detainees. Early in my tenure, I went to breakfast with a foreign ambassador I had known for some time. He opened the meal by graciously offering on behalf of his country to take up to 20 Guantanamo prisoners. I was ecstatic. By the time the meal was done, it was clear that the offer was contingent on the sale of highly advanced military hardware. No deal.

Some leaders liked Obama personally and agreed to take detainees as an act of personal goodwill. I caught a plane to one country after receiving an email from the national security adviser, who had briefly discussed resettling detainees with that country’s president on the margins of a conference. As this president walked me into his offices, he said: “So this is important to President Obama?” When I confirmed that it was, he said: “If it is important to President Obama, it is important to me. We will do it.” The rest of the meeting consisted of pleasantries. Easiest deal I ever did.

By the end of Obama’s time in office, we had largely succeeded in accomplishing our revised mission. Almost 800 individuals had passed through Guantanamo since it opened in 2002, and 116 were detained there when I took office in 2015. But as I drove across the George Washington Bridge on Inauguration Day, only 41 remained. For a few of those, we had negotiated transfer deals that we ran out of time to implement. The remainder included hardened terrorists like Khalid Sheikh Mohammed, who had been (and remains) caught up in yearslong military commission proceedings, hampered by, among other things, the lack of established legal procedures that has plagued their cases from the start.

I was not optimistic that there would be much, if any, progress in the years ahead, but was proud of the hard work we had done to release detainees who had never been charged with a crime and did not pose a threat to our security. As the curtain closed on the Obama administration, we had made progress in reducing the injustice of indefinite detention without charge. But the stain on the United States represented by Guantanamo remained.

I thought little of Guantanamo in the years that followed, partly because of the demands of my legal practice and partly because of the deep freeze that fell over the issue during the Trump presidency. Trump didn’t end up loading up Guantanamo with “bad dudes,” and never acted on his reported impulse to send Americans infected with Covid there. Only a single detainee left the prison (under an agreement negotiated during the Obama administration) and none of the remaining ones became eligible for transfer.

Yet the costs of maintaining the facility continued to grow. By the time Trump took office, the United States was spending hundreds of millions of dollars per year to operate the facility, or approximately $13 million per detainee per year. (Compare that with the annual cost of $78,000 for maintaining a prisoner in the federal Bureau of Prisons, which houses scores of convicted terrorists with no reported security incidents). The facility itself — meant to be temporary when set up in 2002 — was also physically deteriorating.

Then there were the reputational and national security costs. It was no coincidence that when ISIS executed Western hostages, it dressed them in orange jumpsuits evocative of those worn by early Guantanamo detainees. The facility and the imagery associated with it incite hatred against the United States and serve as a recruitment tool for terrorists. That’s why leaders of both parties — including George W. Bush, John McCain, Colin Powell and Condoleezza Rice — came to support its closure, and hundreds of detainees left Guantanamo during Bush’s presidency after he partially reversed course on the matter.

Trump, of course, didn’t care about any of that. Keeping people at Guantanamo was consistent with his desire to get tough on bad guys — even if some of the bad guys were sick, basically as old as he was and unable to be charged with crimes. To be fair, Trump was leveraging the deep politicization of Guantanamo that had taken hold long before he became president. From what had once been a largely bipartisan objective to shut down the facility, Guantanamo became a political football, with Republicans intent on frustrating Obama’s presidency wherever they could.

Some Republican members of Congress admitted in private that the facility should be closed, even as they ranted in public about “releasing terrorists.” The prison endures as a product not just of America’s mistakes in the fight against terrorism but also of the toxic brand of politics that began during the Obama era and have only worsened since.

I began to think again about Guantanamo again in early 2021. We had a new commander-in-chief — one who, as vice president, had been fully committed to Obama’s closure policy. In the four years since Biden had last held office, the world seemed to have moved on even more definitively from the era of the war on terror — a sentiment punctuated by Biden’s decision to complete the withdrawal from Afghanistan by the 20th anniversary of 9/11. The president was committed to reorienting the country toward countering current and future threats, including China.

And yet here we stand on the other side of the withdrawal from Afghanistan, and Guantanamo persists as an anachronistic relic of the prior era. The U.S. national security establishment has a way of operating on inertia for years or decades. In the months leading up to 9/11, when I served on the National Security Council’s counterterrorism directorate, I was surprised to see how many government resources were still oriented toward the defunct Soviet threat. You could count on two hands the number of NSC staff who knew anything substantive about al Qaeda — yet sitting at our desks, I and many others would learn almost instantly of minor seismic disturbances in Siberia.

Guantanamo remains open by virtue of that same inertia. And it is past time to retire this relic of the forever wars. To be clear, I have always believed the United States was right to detain presumed enemy combatants in the early 2000s and to take the most aggressive steps to track down and capture those who attacked us on 9/11. But that was decades ago. The threat environment has fundamentally shifted. Al Qaeda is mostly dismantled — at least, the centralized command and control structure in Afghanistan that attacked us in 2001 is gone. Domestic terrorist groups have become a more pressing threat than foreign ones. And the primary adversaries we now face are nation-states, not the non-state actors we feared in the wake of 9/11.

The detainees themselves are also relics of another time and place. The oldest turns 75 this year. Many stand to die in Guantanamo. What’s more, it’s often forgotten that only a handful of these individuals are accused of direct complicity in attacks that targeted Americans. Many others committed crimes that can be, and long ago should have been, prosecuted in places like Israel, Saudi Arabia, United Arab Emirates, Indonesia, Malaysia or Kenya.

If these detainees had been white and not brown or Black, is there any realistic chance the United States — a country committed to the rule of law — would imprison them without charge for decades? I don’t think so.

In addition to all the old reasons for closing Guantanamo, Biden’s commitment that the United States set a democratic, rules-based example for the world — with human rights as a centerpiece of U.S. foreign policy — provides new impetus. Shuttering the prison will help restore American credibility in the struggle against authoritarianism, which Biden has correctly identified as a principal challenge to democratic governance and U.S. global leadership.

Biden should finish the job Obama started, including, if necessary, through more aggressive steps than Obama took. In particular, he should look for ways to end the stalled experiment with trying detainees through military commissions. He should consider relying more heavily on facilitating foreign prosecutions for tough cases and ultimately releasing detainees who cannot be charged with a crime in this or another country. And to the extent necessary, Biden should look to inherent presidential powers under Article II of the Constitution to finally shutter Guantanamo.

The Biden administration (in which I recently served, but on issues unrelated to Guantanamo) has made some halting progress. In July, the administration repatriated Moroccan national Abdul Latif Nasser, who had spent 19 years at Guantanamo without charge. Nasser was one of the prisoners for whom we negotiated transfer deals in 2016, but which we could not implement before the end of Obama’s term.

Of the 39 detainees now remaining at Guantanamo, a total of 13 are cleared to leave. Fourteen are being held without charge — the so-called forever prisoners. The remaining 12 have been charged but are subject to interminable military commission proceedings — all of which are weighed down by the prisoners’ allegations that they were tortured in U.S. custody.

Those cleared to leave should be transferred as soon as possible through diplomacy led by a senior official with a clear mandate to get the job done. For those who have not been charged by military commissions (and even perhaps for some who have), a sustained effort will be necessary to determine whether it will be possible to build legal cases that can be prosecuted in foreign courts in countries like Israel, Indonesia, Saudi Arabia or the UAE. For both categories of detainee, the process can be slow and occasionally frustrating, but with dedicated staff and high-level attention, it can be done before Biden leaves office.

If Biden succeeds at getting those 27 prisoners out of U.S. custody, the dozen remaining cases will be the toughest. These include Khalid Sheikh Mohammed, the other 9/11 co-conspirators, and those suspected of attacking the USS Cole off the coast of Yemen in 2000. They represent the tough core of the Guantanamo problem, cases familiar to many Americans and whose resolution remains politically fraught. For years, the United States has tried and failed to use military trials to impose death sentences on these terrorists. It is increasingly clear that will never happen.

The case of Majid Khan illustrates why the cases against the 9/11 co-conspirators are going nowhere. Khan pled guilty to a range of charges a decade ago and has been a longtime cooperator with U.S. authorities. This past October, he told the world at his sentencing hearing that the Americans had tortured him — an issue that infects every military commission case. A jury comprised of senior military officers called Khan’s treatment “a stain on the moral fiber of America” and recommended he receive clemency as a result.

Khan’s case forced the United States to confront what it had long sought to avoid: the possibility of a public reckoning with torture and mistreatment of detainees at the hands of U.S. personnel. Instead of confronting this issue through an in-court examination of the mistreatment Khan alleges he endured in U.S. custody (complete with witnesses testifying under oath about barbaric treatment unbecoming of the United States), the government renegotiated Khan’s plea agreement. As a result, Khan should leave Guantanamo as soon as this year when his sentence concludes. The path is now clear for other detainees charged in the military commissions (including in capital cases, which Khan’s was not) to seek similar redress for the treatment they, too, endured.

This means that after almost two decades, it is almost certain that the United States will never be able to extract the punishment it seeks in the 9/11 cases. That we cannot even bring the conspirators to trial is a national embarrassment. But because of our government’s own misconduct, we should give up the illusion that we will ever be able to put them to death.

The Biden administration should instead pursue the only logical way out of this mess: Seek plea agreements that will ensure life imprisonment for the 9/11 and USS Cole conspirators. Striking any sort of deals with those accused of horrific acts of terrorism has been and will remain unpopular. But it will resolve a major part of the unfinished business at Guantanamo, since life sentences can be served in other facilities. Any such plea agreements should be coordinated with the families of the 9/11 victims, and the defendants should be required to cooperate with those families, who are still pursing civil litigation against those who allegedly facilitated the attacks.

Plea deals for the 9/11 conspirators will be politically controversial. But having Guantanamo enter a third decade of operations should be morally unacceptable. To close the facility, Biden should exhibit the same focus on Guantanamo that Obama did, but with even greater creativity for the toughest cases. In doing so, he can close another chapter in the war on terror and move our nation closer to the realization of its democratic aspirations — under the glare of a world watching to see whether the rule of law will endure in America.