Donald Trump’s former White House advisor Stephen Miller was exposed by an investigative journalist on MSNBC on Saturday. Miller, who directed Trump’s border policy during the ex-president’s term in office, has since then be waging his own private war against diversity and programs promoting inclusion. But he wasn’t always like that, according to investigative journalist Jean Guerrero. Guerrero, the author of “Hatemonger: Stephen Miller, Donald Trump, and the White Nationalist Agenda,” appeared on MSNBC to profile the man behind Trump’s border agenda. Want more breaking political news? Click f…