Gee, I don't know why so many people mistakenly believe President Obama is a Muslim. I mean, it's not like it's been repeated in the tabloids (the above is the current issue of Globe), asserted by right-wing leaders (Rev. Franklin Graham notes he was "born a Muslim" and possesses "the seed of Islam") and alluded to passively by everyone from Hillary Clinton (back in the day) to Mitch McConnell (just the other day).
I was fascinated to read that this kind of religious conspiracy theorizing also haunted Abraham Lincoln ("slurred" as a Catholic) and FDR ("slurred" as a Jew). It's never correct, but it correctly exposes which religious group is currently the most loathed.