Obama initially promised to close Guantanamo Bay within a year of entering the White House in 2009. Two days after he was sworn in as president, he signed an executive order mandating a review of the cases of all the detainees. The order also called for the closure of the detention facility. In 2010, a task force concluded that 156 detainees were cleared to be transferred to foreign countries.
The prison, which was opened in January 2002 as Camp X-Ray and has the dubious honour of its 14th anniversary on January 11, currently holds 105 detainees. 
Yet the aims of his executive order have languished since 2009 due to the opposition of Congress, inaction at the Pentagon and other priorities. 

Guantanamo Bay has widely been acknowledged as a stain on America’s international reputation and a recruiting tool for terrorists

Who is challenging the closure of Guantanamo Bay?

Opposition to its closure involves two central issues which Obama has been unable to resolve. One is finding host countries to take in all the detainees. The other issue concerns whether some of the detainees can be moved to "supermax" facilities within the United States.
This becomes a legal mess for the White House. How would the president legally justify holding prisoners indefinitely on US soil? The US administration has not explained how they would get around US law - something it has been able to do in Guantanamo Bay.
The president’s opponents seized on reports that a transferred detainee returned to the battlefield after being released. Abdul Qayum Zakir, who, according to US intelligence, became a Taliban military commander after his release from Guantanamo Bay. In late 2010, an emboldened US Congress passed a law requiring the US secretary of defense to personally certify to Congress that a released detainee "cannot engage or re-engage in any terrorist activity" - which will prove almost impossible to police.
A guard looks out from a tower at the detention facility of Guantanamo Bay US naval base in Cuba [AP]

Are Guantanamo Bay detainees really a threat to the US?

There has also been opposition from the Pentagon. According to reports, US General John Kelly, who oversees Guantanamo Bay, has made it increasingly difficult for foreign delegations to visit the facility, slowing negotiations with third-party countries willing to take detainees.
Tariq Ba Odah, a Yemeni detainee since 2002, was cleared for release in 2009. Even after officials at the US State Department struck a deal with a foreign government to consider taking Ba Odah last year, the Pentagon stalled a request for his medical records for six weeks. Ba Odah remains at Guantanamo Bay and is reportedly severely malnourished from having been on a hunger strike for almost nine years.
Seventeen detainees who have received their final transfer approval are scheduled for release in the coming weeks. As many as an additional 30 more could be released by the summer. This would reduce the prison’s population to 60, but still the question remains: Would the remaining prisoners be moved to prisons in the US, and would their legal status finally be addressed?

Source: Al Jazeera