comment: Ok, I agree it's a poorly-written tune but this opinion is rife with misinformation.
  The base of the melody is not a marching song and predates Sousa by about 75 years. It was written as kind of the theme song for the Anacreontic Society and was originally penned "To Anacreon in Heaven". It's more of a drinking tune, a rabble-rouser if you will.
  The lyrics are about the unsuccessful British bombardment of Ft. McHenry during the War of 1812. Francis Scott Key was inspired that the flag was still standing at the end of the battle, meaning the Americans didn't quit, and wrote the poem "Defence of Fort M'Henry" later adapted using the familiar melodic line.