Nixon would have loved to see Woodward and Bernstein's book shelved in the fiction section, alongside other books of lies like A Million Little Pieces or The Boy Who Came Back from Heaven. (The author's name is Malarkey—of course it's fake.)
But Woodward and Bernstein's story is real, and their investigation into the scandal is as interesting as the scandal itself. As a result, the film mostly follows these two men and their investigation in linear order. Only at the beginning of the film, which depicts the Watergate break-in, do we see a scene that isn't explicitly from their point of view.
Either because Bernstein was more of a jerk in real-life, or because Woodward is played by producer Robert Redford, the movie more closely follows Woodward than Bernstein. Plus, Woodward and Bernstein sounds better than Bernstein and Woodward. Poor Bernstein: always the Garfunkel, never the Simon.
Anyway, Woodward's the first main character we see. He's the first one assigned to the story. He's the one who talks to his shadowy source, Deep Throat. He has doubts about the story's veracity, giving us some internal conflict. Bernstein is more of sidekick, and in fact, is initially shown to be Woodward's rival, if only for a few minutes.
The movie makes a curious choice to stop before Nixon's resignation, instead showing us the news in a quick epilogue. However, Nixon's resignation is a story everyone knows, either from news at the time, from history books, or from the very much fictional film Dick.