Politicians from the same parties, who share ideological policy preferences, are often intensely divided over the tactics best suited to pursue shared goals. This perplexing misalignment suggests that we are missing an important piece of the puzzle. Personality traits provide structure to the many individual differences which shape how each of us evaluate choices in the world around us, and can help explain why ideologically similar politicians can find themselves in stark disagreement over how to behave in office. This research takes advantage of linguistic cues found in politicians’ speeches to rank them on the Big Five dimensions of personality and show how these traits have influence across all aspects of Congress members’ political behavior.