Set in a Democratic presidential primary in Ohio, the plot is direct, and the tempo is as taut as an over-tightened “E” string. Clooney plays the candidate, but Ryan Gosling is the star of this film, the 30-year-old media guru to the candidate’s experienced campaign manager, Philip Seymour Hoffman. These two formidable actors are playing against the other candidate’s campaign manager, the talented Paul Giamatti, and, at times, against each other.