WASHINGTON (Reuters) - White House hopefuls Ted Cruz and Marco Rubio and 13 other Republican U.S. senators on Thursday demanded that Islamic State fighters be sent to the Guantanamo Bay detention center, which would boost its population as President Barack Obama moves to close it. The lawmakers introduced a resolution expressing the need to detain the fighters at the controversial military prison in Guantanamo Bay, Cuba, after reports that U.S. special operations forces had captured leaders of the militant group. “There should be no confusion in the minds of our enemies that, if captured, they will be sent to the detention facility in Guantanamo Bay to be interrogated,” Rubio said in a statement.  Rubio, Cruz, billionaire front-runner Donald Trump and Ohio Governor John Kasich face off in a presidential debate on Thursday night in Miami. The resolution was led by Senator Steve Daines. In addition to Rubio and Cruz, the co-sponsors were Senators Jerry Moran, Cory Gardner, Tom Cotton, Mark Kirk, Orrin Hatch, Joni Ernst, Johnny Isakson, John Boozman, Pat Roberts, Jim Inhofe, Tim Scott and David Vitter. The measure would be nonbinding but underscores the strong resistance in the Republican-controlled Congress toward Obama’s efforts to close the detention camp. Obama launched a final push to persuade Congress to close the detention center for suspected members of groups such as al Qaeda last month. The Obama administration has been trying for years to make good on a pledge the president made at the beginning of his first term in 2009 to close the facility but has faced stiff political opposition. Republican lawmakers insist the prison is an essential tool for holding and interrogating suspects who threaten the United States. Opponents of the detention center say that holding prisoners for years without charge or trial is a human rights violation that goes against fundamental U.S. values and potentially endangers American military personnel. 