There could also be issues with some of those real-life characters, or their descendants, getting their hackles raised.
Nonetheless, I'm hoping they can get this casting sorted out, and move forward.

The LA Daily News reported today that Warner Bros is having trouble getting some "casting" done for their upcoming adaptation of Alan Moore's WATCHMEN. The film being helmed by Zach Snyder( 300, DAWN OF THE DEAD) certainly has a large cast of look a likes to incorporate into the film.
Richard Nixon, Henry Kissinger, H.R. Haldeman, Ted Koppel, John McLaughlin, Annie Liebowitz, John Lennon and Yoko Ono, Fidel Castro, Albert Einstein, Norman Rockwell, JFK and Jackie Kennedy, Andy Warhol, Mao Tze Tung and Larry King.
Alan Moore's WATCHMEN focuses on an alternate universe's version of the United States.