Critics of a possible transfer of Taliban prisoners are discussing tactics to block it, even before the Obama administration appears to have made a final decision on the most politically contentious element of its bid to broker an Afghan peace deal.
Administration officials have, under strict conditions of secrecy, briefed senior lawmakers dealing with military, foreign policy and intelligence issues about the proposal that would move five senior Taliban detainees at the Guantanamo Bay military prison in Cuba to Afghan custody.
But the White House has not yet initiated a formal, 30-day congressional notification process required by a new U.S. law, officials on Capitol Hill said.
Doing so would put the United States closer to implementing a set of confidence-building measures the Obama administration hopes will pave the way for an eventual deal between the Afghan government and the Taliban, who were ousted in a U.S.-led invasion in 2001.
Among detainees who officials say have been earmarked for possible transfer is a former Taliban commander, Mullah Mohammed Fazl, alleged to be responsible for killing thousands of Afghanistan's minority Shi'ites.
The potential hand-over of Fazl, a high-risk detainee who was in the first group of detainees sent to Guantanamo in early 2002, has set off alarms in Congress and among some U.S. intelligence officials.
Some members of Congress have already sent classified letters challenging the administration's tentative release plan. Congressional sources said moves to stymie a prisoner transfer could include attachment of blocking amendments to unrelated legislation.
It's hard to envision that if they transfer really dangerous guys to a really dangerous place, there won't be a fight, a congressional staff member familiar with detainee policy said on condition of anonymity.
The same staff member said concerns also included where any such detainees might end up even if they were handed over to the Afghan government, given its poor track record of security. It's not a cut-them-loose option, the staff member said.
Last April, hundreds of prisoners escaped from a jail in southern Afghanistan through a tunnel dug by the Taliban.
Among the objections to a prisoner transfer, especially among Republicans, is evidence that some released Guantanamo detainees have returned to the battlefield.
While the mechanics of a prisoner transfer remain unclear, it would mark a significant step forward in U.S. efforts to bring a decade of bloodshed in Afghanistan to an end. The efforts got a boost this week with news the Afghan Taliban had reached a preliminary agreement to set up a political office in the Gulf nation of Qatar.
By law, the administration must notify congressional intelligence committees which detainees it intends to transfer and specify where a detainee is being sent and if the United States paid the receiving country money as part of the deal.
The administration must also certify to several committees that the Defence and State Departments and director of national intelligence assess that the countries accepting detainees meet certain requirements. Those include not being a state sponsor of terrorism and ensuring former detainees will not pose threats to the United States.
The administration can waive some of the certification requirements, including a guarantee the prisoner will not re-engage in terrorism, on national security grounds.
Democrats are more likely to support President Barack Obama's peace bid. The White House's desire to draw down U.S. forces in Afghanistan is fuelled partly by fiscal pressures and a widespread belief the war cannot be won on the battlefield alone.
A senior congressional Defence aide said reaction to any Taliban release plan depended on who would get custody, at least initially, of the Taliban detainees and where.
There are people up here who are going to criticize no matter what. There will be a lot of people who will say, 'I'm against this - this is only going to embolden the Taliban,' the aide said.
Yet Congress ultimately has little power to delay or stop planned detainee releases, other than its ability to pass new legislation, which would have to be approved by both chambers and signed by the president.
Still, Obama might be risk-averse as he heads toward the November election. One Democratic congressional staff member, also speaking on condition of anonymity, said the administration signalled last year it would not go ahead with the transfer if it generated significant opposition in Congress.
(Additional reporting by Warren Strobel; Editing by Peter Cooney)