The US President, Donald Trump's former chief strategist has reportedly been subpoenaed to appear before a grand jury investigating Russian influence during the 2016 presidential election. Steve Bannon was identified as a key source for Author Michael Wolff's book "Fire and Fury" on President Trump's first year in office. In it, the President's cognitive abilities came into question but White House doctor Ronny Jackson has just given President Trump a clean bill of health in his annual check-up. CEO of the US Studies Centre Professor Simon Jackman speaks to ABC's Ali Crew about the book, President Trump's health check-up and the Russia investigation.