Why do people still think Barack Obama is a muslim?

Why are there still people calling Barck obama a muslim? Hes not, hes christian. And even if he was muslim so what? Islam isn't anymore violent then christianity. (only the fringe minority of extremist muslims are violent, they could be compared to Evangelical Christians. the difference is we don't take it to violent extremes) I don't understand this hugh emphasis on religion of a candidate. Every time a candidate governs using religion bad things happen. look at the last 8 years.