From the opening paragraph or so from Wikipedia under the subject "Obama":
Obama previously served as a United States senator from Illinois, from January 2005 until he resigned following his victory in the 2008 presidential election.
Who did "O" replace? Bush.
When did the replacement happen? Jan. '09
Bush was in office from:
January 20, 2001 – January 20, 2009
By the looks of things, assuming that Wikipedia has it right, "O" was a Senator for less time than "W" was President...all at the same time!
Surprised?
"O" made his statement as part of his bid up to the Presidential Race...a bit like knowing which way the wind's blowing before taking a decisive stance...

(Problem is...he probably didn't have any idea what was really going on...his puppeteers fed him everything he knew/knows via teleprompter) No real knowledge needed except for being able to read and pronounce words correctly...at the same time...and to look sharp and snappy at the same time too!