Stephen Sackur is at the 2017 Hay Literary Festival to speak to the US Senator Bernie Sanders - the longest serving independent in US congressional history. He was credited with injecting passion and belief into the race for 2016’s Democratic presidential nomination - a race that was eventually won by Hillary Clinton. But did he plant the seeds of a political revolution in the United States?(Photo: Senator Bernie Sanders (D-VT) react during a news conference on release of the president"s FY2018 budget proposal, 2017. Yuri Gripas /Reuters)