It’s 20 years since the twin towers of New York's World Trade Center were reduced to dust and ash. This week, the US is again immersed in memories of the attack and what came after. In 2011, on the 10th anniversary of the 9/11 attacks, Stephen Sackur spoke to the man who was mayor of New York City on that fateful day, Rudy Giuliani. His response back then earned him the title “America’s Mayor”; a decade later, HARDtalk invited him to reflect on how he and his country had been changed by the horrifying events of 9/11.