Trivia: Monroe Cole states that people will be calling him Mr. President for the rest of his life. While it is true people do tend to call former presidents by that title (thus not a movie mistake), as a point of trivia; is it incorrect to address a former president as "Mr. President" or "former president (surname)." While Cole doesn't have to worry about his ex-wife taking his title, leaving office will do that. It's the media that perpetuates this presidential title error.
Trivia: Gene Hackman's final film before he retired from acting. Since this movie came out, the only film or TV projects he's done have been a handful of documentaries, either appearing as himself or narrating.
Answer: His decision to retire wasn't related to this film; it just happened to be his last. He was working on other projects (mostly writing), and wanted to focus on those. He didn't "officially" announce his retirement from acting until 2008.