Americans think of themselves as heroes during World War II, part of the country that defeated Germany and a ruthless dictator to make the world safe for democracy and persecuted minorities. Adolf Hitler killed two-thirds of Jews living in Europe — an estimated 6 million people — largely while the world watched. The U.S. took in more Jewish refugees than any other country, but it wasn’t enough. That’s because it held strong anti-immigrant and anti-Semitic sentiments among its citizens, Congress members, and U.S. State Department staff. America’s culpability in the Holocaust is the subject of a new Ken Burns documentary series from PBS called “The U.S. and the Holocaust.”