Since Congress is an individualistic institution, members tend to behave differently. There are three theories about how members of Congress vote the way that they do: representational, organizational, and attitudinal.
The representational view is the reasonable assumption that members want to get reelected; therefore they vote to please their constituents. Constituents have a clear view on some issues and a legislator's vote on that is likely to attract their attention. The representational view has a superior quality, that is under certain circumstances - namely, when constituents have a clear view on some issue and a legislator's vote on that issue is likely to attract their attention. Sometimes constituents have a direct influence on voting. A member of Congress can win votes by doing services for constituents or by appealing to the party loyalty of the voters. The representational view can be helpful to members who want to get reelected. If a member is not really interested in getting reelected, but pleasing the constituents he may vote according to the organizational view.
The organizational view is based on the essential to please constituents. Members feel it is important to please fellow members of Congress, whose goodwill is valuable to get things done. Congress responds to cues provided by their colleagues. The principal cue is party. Whatever party a member belongs to explains more about his or her voting record than any other factor. If a matter affects a member's state they can take cues from members of their state's delegation to Congress. If a member feels that he wants to vote for what he believes, he may vote according to the attitudinal view.
The attitudinal view is when members of Congress vote on their own beliefs. The attitudinal is proof that members of Congress vote according to their ideology. The ideology of a member of Congress really affects how he or she votes.