The Twilight Zone

At a meeting in a Washington, D.C. club, several professors hold a discussion on whether it's possible to travel back in time to alter history. One of the men, feeling somewhat faint on his way home, soon finds himself travelled back to the night of Lincoln's assassination. Thinking back to his discussion, he soon decides to try and warn the President, only to be arrested for disturbing the peace. He then realizes that some past events can be changed; others can't.