WASHINGTON—Homeland Security Secretary Kristi Noem is slated to make a trip Friday to Guantanamo Bay, as the Trump administration steps up use of the naval base in seeking to emphasize toughness against migrants it says have criminal backgrounds.

As tents went up in Guantanamo Bay, Cuba to hold migrants, attorneys at the Department of Homeland Security and Pentagon were still trying to determine whether it was legal to take the unprecedented step of flying migrants from the US southern border to the facility,