Lt. Col. JB Brindle, a Defense Department spokesman told CNN:
In order to meet official mission requirements, the Department of Defense is working through appropriate channels in accordance with all applicable legal requirements in order to acquire a limited amount of leased space in Trump Tower. The space is necessary for the personnel and equipment who will support the POTUS at his residence in the building.
Military support for a president requires close proximity to the commander in chief which is why the Pentagon needs to rent a more expensive space closer to the penthouse where Trump resides when he is in New York.
According to Jared Horowitz, who works for the company responsible for rentals in Trump Towers, the floors available to rent with an average floor space between 13,500 to 15,500 square feet, cost about $1.5 million a year. Trump Tower is owned by Trump Organization.
The Defense Department also noted that the military has had to seek similar accommodations in the private residences of previous presidents as well.