I used to think the same. Some elderly people who lived through those times and are now in the US shake their heads and say that they recognize the signs, though. Not long ago I read an article written by an old German lady; perhaps someone can find it?
And I have had talks with an old man who actually was in the German Army as a youngster. He thinks Obama taps into the same well of hysteria and foolish gratitude to which Hitler appealed. He reminded me that though we today see the wartime photos of Hitler and feel revulsion, when Hitler rose to power he was considered handsome, cultured, sweet-natured, reasonable, and charming. The Germans elevated him at a time of great national distress and thought he'd solve their problems, as we have done with Obama. The elevation of a monster can take place in many cultures.
He fell silent then and did not attempt to defend the behavior of the Germans afterward, but I could well imagine certain groups of Americans yielding to the worse aspects of their nature, too.
I am hearing more and more of those anecdotal stories.