According to this, lobbyists and special interest groups don't get what they pay for, at least not at the candidate level.
Contrary to popular belief and typical media portrayals, big campaign contributions and lobbying do not necessarily win the political influence that determines votes in the U.S. Congress. Congressional action is less a function of donations and lobbying than it is of public opinion, ideology, and party affiliation, according to University of Washington sociology professor Paul Burstein, whose work provides insights into the legislative process.
In the summer 2003 issue of Contexts magazine, published by the American Sociological Association, Burstein reports on research that undermines the pervasive cynicism cultivated by the mass media and citizens' "common sense" perceptions. While most Americans believe that the government is run for the interests of a few rather than for the benefit of all, most major studies show that money and special interest groups have little influence on policy.
"Party and ideology matter far more than campaign contributions and lobbying… The power of interest groups to get legislators to change their votes in the face of personal ideology and party commitments is real but very limited," wrote Burstein.
Pretty interesting stuff. I guess they should focus on party-wide donations.