Sometimes politicians don’t speak the truth because they just don’t know better such as when Obama said he had travelled to all 57 of the United States not including Alaska and Hawaii, and still had "one left to go." Hmm … maybe he was referring to the 57 Arab states.
However, most of the time when a politician tells tall tails it’s on purpose such as Nancy Pelosi when she said she was not briefed by the CIA about enhanced interrogation techniques.
Winston Churchill called these falsehoods terminological inexactitudes.