Define and differentiate political parties and interest groups. Why does the U.S. have a two party system? In your informed opinion, should the U.S. remain a two-party system or shift to a multiparty system? What is being balanced here? Do you see a shift in the party system happening? Identify four types of interest groups. Are you a member of an interest group or political party? Why/why not? Are political parties or interest groups more powerful? Why? .