NEW: Karoline Leavitt says she and President Trump have reviewed newly released FBI surveillance footage of a potential subject outside Nancy Guthrie's home: "I was once again with the president. He and I were both reviewing the newly released surveillance footage from FBI in the Savannah Guthrie case on just this heartbreaking situation with respect to her mother." "The president encourages any American across the country with any knowledge of this suspect, to please call the FBI, who continue to assist state and local authorities who are leading this investigation on the ground." "The prayers of this entire White House are with Savannah and her family at this time."