Elected officials are always concerned with public opinion, which is why political scientists have developed so many tools for measuring it. Politicians will often test the popularity (or unpopularity) of potential legislation before undertaking it. This is obviously because, in a democratic society, politicians can be voted out of office if they are unpopular. But politicians are not totally at the mercy of public opinion—they can help shape it through spending on advertisements, appearances on news broadcasts, and public speaking engagements.

Interest groups are very important in American politics. They can take several forms, but the most prominent in the United States are interest groups that represent the interests of a single group. Their role is to ensure through raising money, hiring lobbyists, and conducting publicity campaigns, that the issues that concern their members are addressed in national and state politics. The National Rifle Association (NRA) is a very powerful and controversial interest group. They use their influence to oppose restrictions on guns and to promote the interests of gun owners.

The role of political parties is to get their members elected. The two major parties in the United States stand on two different ideological platforms. These sets of beliefs are generally shared by their members and by the people that the parties support in elections. Parties nominate candidates through primary elections and back these candidates financially. Ideally, a party's candidate is one who has been "vetted" by the party and who party supporters can feel comfortable voting for. Because of the expense of American politics, as well as the primary system and the "winner-take-all" system of elections, it is very difficult for people outside the two major parties to get elected.