We have all kinds of dangerous Americans in prison.
Republicans have brainwashed people (including, sadly, a bunch of Democrats) into believing that about 200 terrorism suspects can't be housed in American prisons.
These terrorism suspects don't have super-powers. They've not going to jump over the fences, mind-control all the guards or create an atomic bomb out of their tea. So why not house them in American military jails? Didn't we manage Germans and Japanese in American military jails without having them invade America? Maybe Americans were just smarter and braver during World War II.
I suspect the majority of the people remaining in Guantanamo probably do have ties to terrorism. We've released nearly 500 "terrorists" from Guantanamo over the last seven years because there was inadequate evidence (even by Bush administration "standards") to hold them.
What should happen is that the remaining terrorism suspects should be moved to at least two American military prisons and they should be tried. If they're innocent, they should be returned to their countries. If they're guilty, they should serve out their term in an American military prison. Obama has forcefully stated that America won't continue the heinous practices of the Bush administration, including terrorism. But holding terrorism suspects indefinitely in a third-party country has seemed, frankly, as un-American as engaging in torture.