Congress has carved out an exemption to the National Historic Preservation Act, in order to allow presidents to make needed changes. The current Oval Office has existed since the early 1930s, after its conception by President Franklin D Roosevelt.
Greg Werkheiser, from the law firm Cultural Heritage Partners, which specialises in historic preservation, says that temporary alterations like "furniture and decor is completely up to the president's discretion".
"As long as they're not damaging the permanent art and architecture, they can generally do whatever they want," he told the BBC.

