President Donald Trump promised more than a year ago to hold 30,000 migrants at the notorious Guantanamo Bay military base, but it now sits almost empty, according to a new report. Just six migrant detainees were being held at the U.S. naval base in Cuba on Monday, CBS News reported, citing federal documents. All of the detainees are from Haiti. Despite the small number of detainees at Guantanamo Bay, the operation is expected to cost the military more than $70 million, according to information provided to a Senate Democrat. Trump had vowed to send tens of thousands of migrants from the U.S. to Guantanamo Bay shortly after returning to the White House.…