The last two prisoners to leave the U.S. detention center at Guantánamo Bay were dead. On February 1, Awal Gul, a 48-year-old Afghan, collapsed in the shower and died of an apparent heart attack after working out on an exercise machine. Then, at dawn one morning in May, Haji Nassim, a 37-year-old man also from Afghanistan, was found hanging from bed linen in a prison camp recreation yard.

In both cases, the Pentagon conducted swift autopsies and the U.S. military sent the bodies back to Afghanistan for traditional Muslim burials. These voyages were something the Pentagon had not planned for either man: each was an "indefinite detainee," categorized by the Obama administration's 2009 Guantánamo Review Task Force as someone against whom the United States had no evidence to convict of a war crime but had concluded was too dangerous to let go. Today, this category of detainees makes up 46 of the last 171 captives held at Guantánamo. The only guaranteed route out of Guantánamo these days for a detainee, it seems, is in a body bag.

The responsibility lies not so much with the White House but with Congress, which has thwarted President Barack Obama's plans to close the detention center, which the Bush administration opened on January 11, 2002 with 20 captives.

Congress has used its spending oversight authority both to forbid the White House from financing trials of Guantánamo captives on U.S. soil and to block the acquisition of a state prison in Illinois to hold captives currently held in Cuba who would not be put on trial -- a sort of Guantánamo North. The current defense bill now before Congress not only reinforces these restrictions but moves to mandate military detention for most future al Qaeda cases unless the president signs a waiver. The White House withdrew a veto threat on the eve of likely passage Wednesday, saying the latest language gives the executive enough wiggle room to avoid military custody.

On paper, at least, the Obama administration would be set to release almost half the current captives at Guantánamo. The 2009 Task Force Review concluded that about 80 of the 171 detainees now held at Guantánamo could be let go if their home country was stable enough to help resettle them or if a foreign country could safely give them a new start.

But Congress has made it nearly impossible to transfer captives elsewhere. Legislation passed since Obama took office has created a series of roadblocks that mean that only a federal court order or a national security waiver issued by Secretary of Defense Leon Panetta could trump Congress and permit the release of a detainee to another country.

Neither is likely: U.S. District Court judges are not ruling in favor of captives in the dozens of unlawful detention suits winding their way from Cuba to the federal court in Washington. And on the occasions when those judges have ruled for detainees, the U.S. Court of Appeals has consistently overruled them in an ever-widening definition of who can be held as an affiliate of al Qaeda or the Taliban.

Meanwhile, Defense Department General Counsel Jeh Johnson, the Pentagon's top lawyer, believes that Congress crafted the transfer waivers a year ago in such a way that Panetta (and Robert Gates before him) would be ill-advised to sign them. (In essence, the Secretary of Defense is supposed to guarantee that the detainee would never in the future engage in violence against any American citizen or U.S. interest.)

In a strange twist of history, Congress, through its control of government funds, is now imposing curbs on the very executive powers that the Bush administration invoked to establish the camps at Guantánamo in the first place. Much of its intransigence is driven by the politics of fear: what if, for example, a captive is acquitted in a civilian trial because the judge bars evidence obtained by the military without benefit of counsel? When will another freed Guantánamo detainee attack a U.S. target or interest, such as when Abdullah al Ajami, who was transferred to Kuwait in 2005, blew himself up in a truck bomb attack in Iraq in 2008?

In the face of such public and political pressure -- especially from Congress -- Obama administration officials have waffled at several key moments. For example, Holder changed his mind on where to try five alleged 9/11 plotters at Guantánamo, including Khalid Sheikh Mohammed. In November 2009, Holder announced that the trial would be held in a civilian courtroom in Manhattan; then, in April 2011, following strong resistance from congressional representatives and New York politicians, the White House abandoned this plan and instead announced that Pentagon prosecutors would bring a trial by military commission.

Resettling in the United States those captives cleared for release has also become taboo. Soon after taking over in 2009, the Obama administration was considering resettling Guantánamo captives from China's Uighur Muslim minority, whom the Bush administration had readied for release. (They were to be hosted by Uighur-Americans in Virginia.) But then, in the face of congressional objections, the White House lost its nerve. The United States instead scattered the Uighurs to Bermuda, Switzerland, and even the Pacific island nation of Palau; five more Uighurs remain at Guantánamo.

Factors besides Congress also contributed to the current Guantánamo stalemate. First, the Defense Intelligence Agency concluded that at least a fourth of the detainees the United States has released from Guantánamo were confirmed or suspected of later engaging in terrorism or insurgent activity. Opponents of closing Guantánamo immediately seized on these figures. (For its part, the Obama administration noted that most of those on the recidivist list were transferred before Obama took office, when the Bush-era Pentagon approved some 500 releases. Officials took fault with these big-batch transfers and claimed that the Obama administration's individually fashioned, case-by-case system for release would yield better results.)

Second, over the past couple years a powerful al Qaeda offshoot has taken hold in Yemen, the very country where the Obama administration had planned to transfer many detainees. Sending dozens of suspected terrorists back to a country besieged by a growing terrorist threat is hardly good politics or security policy.

Lastly, Obama's executive order to close Guantánamo was undone by the burdensome bureaucracy of the task force, which sought to sort each captive's Bush-era file. Each detainee's case file contained competing and often contradictory assessments from the Defense Intelligence Agency, the Pentagon's Office of Military Commissions, the Department of Justice, and myriad other offices, bogging down the review process. Time ran out before the task force could settle on a master plan to move the detainees out of Guantánamo in time for Obama's one-year deadline.

Now it's the war court -- the military commissions that the Bush administration created to hear war crimes cases at Guantánamo, which were reformed by Obama through legislation -- or nothing. And only two cases, both proposing military executions, are currently slated to go before the Guantánamo tribunals: those for the 9/11 attacks and for the October 2000 bombing of the U.S.S. Cole. To date, the war court has produced six convictions, four of them through guilty pleas in exchange for short sentences designed to get the detainees out of Guantánamo within a couple of years.

Still, in the Kafkaesque world of military detention, neither an acquittal at the war court nor even a completed sentence guarantees that a detainee gets to leave Guantánamo. Once convicted, a captive is separated from the other detainees to serve his sentence on a different cellblock. (Four are there today, only one serving life.) Once that sentence is over, as both the Bush and Obama administrations have outlined detention policy, the convict can then be returned to the general population at Guantánamo as an "unprivileged enemy belligerent."

The doctrine has yet to be challenged. But if Ibrahim al Qosi, a 51-year-old Sudanese man convicted for working as a cook in an al Qaeda compound in Kandahar, does not go home when his sentence expires next year, his lawyers are likely to turn to the civilian courts to seek a release order.

Guantánamo has largely faded from public attention. There is little reason to expect it to emerge as an issue in the upcoming presidential campaign season beyond the usual finger-pointing and slogans: Obama may blame Congress for cornering him into keeping the captives at Guantánamo rather than moving them somewhere else, and his opponents will no doubt argue that, by virtue of his wanting to close the facility in the first place, Obama is soft on terrorism. ("My view is we ought to double it," Mitt Romney said about Guantánamo in a 2007 debate.)

Meanwhile, the detention center enters its eleventh year on January 11. Guantánamo is arguably the most expensive prison camp on earth, with a staff of 1,850 U.S. troops and civilians managing a compound that contains 171 captives, at a cost of $800,000 a year per detainee. Of those 171 prisoners, just six are facing Pentagon tribunals that may start a year from now after pretrial hearings and discovery. Guantánamo today is the place that Obama cannot close.