Former U.S. Ambassador to the United Nations Nikki Haley said on Thursday there was room for only one president at a time as she blasted Chairman of the Joint Chiefs of Staff Gen. Mark Milley for going behind former President Trump 's back with calls to his Chinese counterpart. 'You don't have the back of the Chinese, you have the back of your president,' she told Fox News . Hers is the latest Republican voice to condemn Milley amid reports he told his Chinese counterpart he would warn him if Trump decided to attack China . Critics have accused him…