What is the function of interest groups in the U S political process?

Interest groups attempt to influence politicians so that they act in the best interests of their group. They do this through advertising, lobbyists, political contributions, and other means. They advocate for a cause, industry or organization in much the same way that a lawyer advocates for a client. Ideally, conflicting interest groups will advocate for their respective causes, providing a lawmaker with enough information to make an informed decision one way or the other.

If an interest group is able to gain access to a politician through the use of a lobbyist, they will be able to argue their position with that politician on a one on one basis. On the plus side, this can give the politician access to information that he might not have received otherwise. However, it can also give an interest group a disproportionate amount of influence which can benefit the interest group at the expense of the general public, especially if the interest group is able to contribute large amounts of campaign money or has well organized blocks of voters who can affect the outcome of an election.