Factual error: A scene near the beginning of the movie when Forest Whitaker and Oprah are both speaking on different phones. The phone that Forest is using has a modular plug. The scene takes place during the Kennedy administration (early 60's). The modular phone plug was not patented and put into use until 1975.
Factual error: A concrete barrier is shown around the White House in the 1960's. This was not put into place until the 1980's.
Factual error: Early in the film there is a shot of the White House that is supposed to be from the 1950's. If you look closely towards the street in front of the White House at the bottom of the screen you can see modern day cars going by. (00:22:25)
Other mistake: When Cecil and Gloria are having their birthday celebration, before they are informed of Charlie's death, Cecil goes to the refrigerator to open a bottle of champagne. We hear the distinct pop of a cork from a bottle of sparkling wine, so we know he chose that bottle, but when he enters the living room a few seconds later, he is holding a glass of non-sparkling wine (no bubbles are visible).