The fractures in American society are widening; over guns, abortion, education and more. But the deepest, most traumatic fracture is surely over race. The US is post slavery, post segregation, but definitely not post-racism. Stephen Sackur speaks to Ibram X. Kendi an influential writer and academic who argues the only way to not be racist is to be actively antiracist - a message he says children must hear. Is his approach bound to intensify America’s internal conflict?