Hitler's overriding characteristic was his insane nationalism, murdering millions, and attempting to enslave the world to his Aryan philosophy. Yes, there are some similarities with Obama, but no comparison to Hitler can ever be valid unless it's to another powerful psychopath such as Stalin or Pol Pot because this behavior overwhelmingly overshadowed everything else he was or did. Similar if somewhat less apparent comparisons were made of Bush and Hitler, but it's like saying someone is like Charles Manson because he plays the guitar, or claiming that an elephant is like a snake because of its trunk. While one can find similarities with Hitler in many people, these are so incidental compared to Hitler's noteworthy characteristics as to detract from one's argument rather than enhance it. Always.
Everyone knows this.