What small mistake did Barack Obama make during his proceedings?

Answer 1

I am not sure which "proceedings" you are asking about. All presidents make mistakes, and Barack Obama is no exception. If you are talking about the mistake when taking the oath of office in January 2009, that was not his mistake: Chief Justice John Roberts read the oath incorrectly and Mr. Obama repeated it incorrectly as a result. To make sure everything was the way it was supposed to be, the president was asked to re-take the oath the next day, and this time, it went off perfectly.