Twenty years after leading the impeachment efforts against Bill Clinton, Ken Starr made his debut on the Senate floor in defence of Donald Trump, while two Republican senators admit that John Bolton's testimony is becoming "increasingly likely" following bombshell revelations in the former national security chief's book.The president reacted angrily after the manuscript Mr Bolton's book was leaked in which the former aide claims the president told him the decision to withhold military assistance to Ukraine last summer was explicitly tied to demands for an investigation into Joe Biden.