President Trump is replacing National Security Adviser General H. R. McMaster, despite a tweet last week from the White House claiming the two have a good working relationship. Trump tweeted Thursday that former US Ambassador to the UN, John Bolton, will take over the post next month. The 69-year-old Bolton served the Reagan and Bush administrations. Many experts question his suitability for the role of national security head as he's well known for his hawkish stance. Bolton will be Trump's third national security adviser. This is the latest shake up in the senior ranks of the Trump administration, following the axing of Rex Tillerson as Secretary of State early this month.