Structure is a huge part. Local projects (infrastructure being a common one) used to get a lot of funding via earmarks. Say you have a senator who's constitue

Structure is a huge part. Local projects (infrastructure being a common one) used to get a lot of funding via earmarks. Say you have a senator who's constituents don't care one way or the other about your bill but their party affiliation requires them to vote against your bill. You toss them an earmark that they can use to say "look at how I've helped you" to his constituents next election with the understanding that he'll break from his party's default position on your bill.