YOUNGSTOWN, OHIO - Republican presidential nominee Donald Trump said on Monday that the US Federal Reserve is keeping interest rates low to prevent an economic downturn and "at some point" the rates must change."They're keeping the rates down so that everything else doesn't go down," Trump said in response to a reporter traveling on his plane who asked him to address a potential rate hike by the Federal Reserve in September. "We have a very false economy," he said."At some point the rates are going to have to change," Trump, who was campaigning in Ohio on Monday, added. "The only thing that is strong is the artificial stock market," he said.