Daniel Day-Lewis is the front runner to win the "Best Actor" Oscar at this year's Academy Awards for his depiction of Abraham Lincoln. Not to take anything away from his performance, but it's much tougher when audio and visuals of the person are available and fresh in some viewers minds. Will Smith as Muhammad Ali, Denzel Washington as Malcolm X, and Ingrid Bergman as Golda Meir all impressed with their roles of people whom audiences had seen speaking on their television sets in the news, if not in person.
I dare say that Anthony Hopkins probably had more liberty playing Saint Paul in the Peter and Paul mini-series than he did playing Richard Nixon or Alfred Hitchcock in later movies, since audiences have no frame of reference for the physical appearance, body language, or vocal inflections of Paul of Tarsus, but have probably seen much documentation of the American president and the iconic film director.
It's always interesting to see actors tackle the challenge of bringing a real person to life in a dramatized story based on actual events. When they make us forget their celebrity status and start to believe that we're watching the real deal, it's evidence of an acting job well done.