nth Chess.com Tournament

Someone throw me a bone here. I suggested that Bill Clinton was 'Mr. ex-President'. "No, no, no!", I was told. "You have to call him: 'Mr. President' ". Is he - or is he not, Mr. President? Let's have a definitive answer. This could be important. Which (if either) of my two earlier statements is incorrect?

1. Mr. President is the head of state http://en.wikipedia.org/wiki/President_of_the_United_States
2. Bill Clinton is Mr. President {if I interpret ozzie_c_cobblepot correctly}

Former Presidents are entitled to the Honorific of Mr. President for their life span even if they no longer have the position.  This is similar to the useage for titles such as Senator, Governor, Judge, Ambassador, General, etc.  Thus Bill Clinton is an ex-President who is correctly addressed as Mr. President or President Clinton.  Our substitue for a peerage I guess.