WASHINGTON -- President Barack Obama's hardest sell in his renewed push to close the U.S. detention center at Guantánamo Bay, Cuba, may be members of his own party - moderate Senate Democrats facing tough re-election bids next year in the strongly Republican South.

Obama has stepped up the pressure to shutter the prison, driven in part by his revised counterterrorism strategy and the 4-month-old stain of the government force-feeding Guantánamo prisoners on hunger strikes to prevent them from starving to death. Civil liberties groups and liberals have slammed Obama for failing to fulfill his 2008 campaign promise to close the installation and find another home for the 166 terror suspects being held there indefinitely.

Republicans and some Democrats in Congress have repeatedly resisted the president's attempts to close the facility, arguing that the prisoners are too dangerous to be moved to U.S. soil, that Guantánamo has a perfectly adequate prison and that the administration has failed to offer a viable alternative.

White House counterterrorism adviser Lisa Monaco lobbied House members in advance of several votes last month to no avail. The House delivered strong votes to keep open the prison and to prevent Obama from transferring detainees to Yemen. Separately, the president's recent appointment of a special envoy on Guantánamo, Cliff Sloan, has met with a collective shrug on Capitol Hill.

In the coming weeks, the Senate will again vote on the prison's future. All signs point to a bipartisan statement to keep the facility open despite a recent vow to end detention at the installation by two national security leaders - Sens. Dianne Feinstein, D-Calif., and John McCain, R-Ariz.

"When you go out, you talk to average Americans about it, they want to keep them there, they want to keep the terrorists there, they don't necessarily want to hold them here," said Sen. Kelly Ayotte, R-N.H., a fierce proponent of keeping Guantánamo prison open.

Ayotte, who plans to push legislation on a sweeping defense policy bill later this summer, is likely to attract support from Republicans as well as several Democrats looking ahead to tight Senate races next year in Arkansas, Louisiana and North Carolina. Votes on the detention center will give these Democrats a high-profile chance to split with a president who is extremely unpopular in parts of the South.

Consider Sen. Mark Pryor of Arkansas, one of the most vulnerable incumbents in next year's congressional elections.

Last November, he was one of nine Democrats to vote for prohibiting the use of any money to transfer terror suspects from Cuba, backing an amendment by Ayotte. The Senate easily passed the measure, 54-41, as part of the defense policy .

Last month, a potential Republican challenger to Pryor, Arkansas Rep. Tom Cotton, was one of a handful of speakers during House debate on the issue. Obama is pushing to transfer approved detainees - there are 86 - to their home countries and lift a ban on transfers to Yemen. Fifty-six of the 86 are from Yemen.

Cotton, an Iraq and Afghanistan war veteran, pleaded with his colleagues to "ensure that terrorists at Guantánamo Bay do not escape back onto the battlefronts of the war on terror."

Asked recently whether he favors keeping the prison opened or closed, Pryor said simply, "Open."

Louisiana Sen. Mary Landrieu, another Democrat who voted last year to keep the facility open, indicated she's unlikely to change her position.