Hillary Clinton is firm favourite to win the Democratic Presidential nomination and then go on to become the next US President at the election in November 2016, according to the latest polls. What are the challenges facing candidate Clinton?  And can she return to the White House – this time as America’s first female President? Also in this edition of Between the Lines, another in Tom Switzer’s occasional series reflecting on the lessons from pivotal moments in our history. This week, Tom considers whether action by the United Nations, Europe or the US could have prevented the Srebrenica massacre 20 years ago this weekend.