US President Barack Obama's unfulfilled promise to close Guantanamo Bay is a lesson in how soaring campaign vows can wilt in the partisan stew and entrenched obstructionism of Washington politics.

Stalled efforts to close the war on terror camp also reflect the intricate, and often immovable homeland security state built by ex-president George W. Bush which endures even as memories fade of the September 11 attacks of 2001.

The US base at Guantanamo Bay, Cuba accepted its first prisoners from the newly drawn battlefields of the global war on terror on January 11, 2002.

A decade on, 171 prisoners remain, most in legal limbo, some awaiting transfer abroad and at least 40 may never face justice but are deemed too dangerous to ever be freed.

Seeing Guantanamo as a stain on America's image, a rebuke to its founding values and a "recruiting tool" for Al-Qaeda, Obama ordered the facility closed within a year, in the first frenetic hours of his presidency in January 2009.

A few months later, at the National Archives in Washington, Obama declared : "there are no neat or easy answers here. But I can tell you that the wrong answer is to pretend like this problem will go away if we maintain an unsustainable status quo."

"As President, I refuse to allow this problem to fester. Our security interests won't permit it. Our courts won't allow it. And neither should our conscience."

But the rookie commander-in-chief learnt the limits of presidential power, struggling to establish a new legal system to process suspects as it became clear Congress did not share enthusiasm for closing Guantanamo.

Obama "made a big political miscalculation," said Julian Zelizer, a professor of history at Princeton University, who added "political blowback" including from Democrats forced Obama to climb down on the closure plan.

Lawmakers of both parties opposed bringing Guantanamo inmates to their own districts for trial or detention. And Congress repeatedly limited funding to transfer any inmates to the US mainland, a prerequisite for closing the camp.

An outcry also forced the administration to abandon plans to use the civil legal system in New York to try Khalid Sheikh Mohammed, confessed mastermind of the September 11 attacks in 2001.

Mohammed and co-conspirators will now face military tribunals in Guantanamo.

Complicating Obama's efforts to empty the camp, his administration no longer sends Yemeni prisoners home to a nation that is a hot front in the US battle with Al-Qaeda -- leaving them languishing in Guantanamo cells.

In March 2011, in a nod to political realities, Obama signed an executive order allowing retooled military commissions at Guantanamo to try inmates for war crimes.

He also ruled that inmates held indefinitely -- pending an unlikely end to the US "war on terror" -- should be granted periodic reviews and pledged to uphold international standards on detention.

The administration also fought to preserve the right to use federal courts to try some suspects, rather than exclusively using military justice.

But critics say Obama has effectively prolonged Guantanamo's life.

"Guantanamo remains a potent symbol of injustice and a stain on America’s reputation," said Elisa Massimino, president and CEO of Human Rights First.

"Past violations of the Geneva Conventions at Guantanamo have marked it around the globe as a symbol of a great nation setting aside its laws and values for the sake of expediency."

Aides say Obama remains deeply committed to closing Guantanamo and still believes its presence is a detriment to US national security.

But there is no obvious political route to closing it, and as he seeks reelection, Obama may perhaps steer clear of such an intractable issue.

He may have some breathing room: political pressure to shutter Guantanamo which burned in Democratic souls in 2008 seems to have abated. And he can argue in mitigation he kept another core campaign promise -- ending the Iraq war.

Guantanamo's longevity also shows the tenacity of the homeland security structure laid down by Bush, which included Guantanamo, battlefield swoops for terror suspects and expanded surveillance and wiretapping.

"It is a legacy that is going to last a long time, outliving his presidency, outliving his successor's presidency," said Zelizer.

And Obama has shown a taste for flexing executive power himself, pursuing a relentless airborne war with drones against terror suspects that some experts believes gets into shady legal ground.

Some campaigners hope that if Obama wins a second term, he may try again with Guantanamo. But he might judge four more years to be better spent in bolstering his economic legacy.

And a Republican president seems unlikely to act: party frontrunner Mitt Romney is on record as vigorously supporting Guantanamo's continued existence.

"The politics surrounding Guantanamo are certainly toxic, but this underscores the need for leadership from the top," said Massimino.

"Political space is never ceded without leadership, and a fight."