The United States has started sending more migrants deemed by officials to be “high threat” criminal aliens to the U.S. naval base at Guantanamo Bay, Cuba, just days after emptying out the base’s migrant facilities.

The base had been cleared of migrants since Thursday, after the government sent 177 to Venezuela and one back to the United States.

A group of five Senate Democrats led by Sen. Dick Durbin (D-Ill.) sent a letter to President Trump on Monday challenging his transfer of migrants to detention centers at the U.S. Naval station in Guantánamo Bay,

The Trump administration has said little about the Venezuelan men who were transferred from Texas to the U.S. military base in Cuba.

Officials at the Department of Homeland Security and the Defense Department are racing to set up multiple tent facilities in Guantanamo Bay, Cuba, to house thousands of migrants, but the scattered efforts have prompted questions internally about who’s in charge and what will happen once people arrive on site.