Sen. Ron Johnson (R-WI) asserted on Sunday that the Guantanamo Bay detention center should remain open, and that the detainees should be held indefinitely without charges because they were "evil."

Late last year, President Barack Obama told CNN that he would do "everything" he could to close the Guantanamo Bay prison by the end of his presidency. The president's administration moved closer to that goal last week when five more detainees were released.

"The people left in Guantanamo Bay are evil people," Johnson told Fox News host Shannon Bream on Sunday. "And they will -- many of them -- return to battle."

"One of the most important things we have to do, we have to have an effective intelligence gathering capability," he continued. "And one of the ways you do that is you capture these unlawful combatants and you detain them. And then over a long period of time, you interrogate them. And that's how you really develop the intelligence to try to foil future plots."

"We've released hundreds of prisoners from Guantanamo. The people there are the worst of the worst, and they should not be released."