Trump says he'll hold undocumented immigrants at Guantanamo Bay

Driving the news: "We have 30,000 beds in Guantanamo to detain the worst criminal illegal aliens threatening the American people," Trump said.

• "We don't want them coming back so we're going to send them out to Guantanamo," he continued.

Zoom in: There were still 15 prisoners being held at Guantanamo Bay as of the Pentagon's Jan. 6 update, but a separate facility will hold immigrants.

• The White House directed the secretaries of Defense and Homeland Security "to take all appropriate actions to expand the Migrant Operations Center at Naval Station Guantanamo Bay to full capacity."

Zoom out: Holding immigrants in facilities is by far the largest cost of the deportation process.

• An Axios review of various estimates put yearly detention costs at $66 billion under Trump's possible mass deportation plan.
• ICE only has about 38,000 people in detention — prioritizing noncitizens the border patrol arrested at the Southwest border and noncitizens with criminal histories, according to ICE's annual report.

A backlog of 3.7 million cases in immigration courts, where immigrants are entitled to make their case to stay in the country, means detained immigrants could wait months, if not years, for their hearing.

• To hold more people from a raid surge would require a mass building project of "soft detention" centers, or temporary facilities, to house people.
• The Trump administration will have to award private contracts to build such detention centers, and offer health care and education to detainees.

Editor's note: This story has been updated with details from the White House's order.

Go deeper: All undocumented immigrants are "criminals," Trump administration says