US President Donald Trump has signed an executive order that he says will prevent future presidents from making certain changes to the White House Oval Office. Trump, a former real estate mogul, has altered the president's official office during his second term, most notably by adding many gold features to its walls. "So we're making it a national monument, and it will not be allowed to be touched by anybody, destroyed, ripped down by stupid people, in order to build something in a slightly different shape," Trump told reporters on Thursday.