It's not corruption, it's prioritizing based on contributions

Shankar Vedantam wrote for the Washington Post:
July 16, 2007

Through the first quarter of this year, according to data about presidential race contributions from the Center for Responsive Politics...

Real estate groups gave Mitt Romney $1.6 million,
Education groups gave Barack Obama $696,000,
Casinos gave Rudy Giuliani $118,000
and the entertainment industry gave Hillary Clinton $794,000.

Richard Hall ... came to Washington on a fellowship to work for then-Sen. Tom Daschle (D-S.D.). Hall and Daschle were fired up about a hunger relief bill that was working its way through Congress...it was an issue the senator cared about deeply, and Hall was enthusiastic to work on an issue that touched his conscience.

As Hall worked on amendments and helped deal with the minutiae of moving a bill through Congress, however, the outlines of a drought emerged in the eastern part of South Dakota.

By the time Hall finished..., he had gotten a lot accomplished to help dairy farmers.

But the hunger relief bill was still sitting on his desk.

...The only problem, of course, is that by focusing on some constituents, the politician no longer has time to focus on issues that help other constituents. Politicians may feel they are in the corner of both wealthy and poor constituents, but the money that flows into politics tends to get them to prioritize the concerns of the wealthy and the organized over those who are marginalized.