I have been thinking about the cause of pork spending (patronage). Patronage is fairly widely regarded as bad for the economy, so why does it persist?
The classic explanation is that patronage gives large benefits to a small population, but spreads costs over a wide population; this would make patronage a classic externality. Every citizen has an incentive to vote for a representative who promises pork projects, even though they realize that they are bad for the country as a whole. This has theory two big problems. First, people mostly vote altruistically. Second, this theory predicts that only the majority party should get patronage spending, the minority party should get essentially nothing and should always vote against patronage (a la Buchanan and Tullock). This is clearly not the way patronage works.
A theory that incorporates voter ignorance and altruism works like this: voters vote altruistically, but because they are ignorant of national circumstances, they vote based off their personal experience. Since representatives who vote for patronage make their state better off, they get reelected, even if patronage is bad for the country as whole. This theory is better, but still not completely correct.
The thing that both of these stories miss is that the legislature can always make rules for itself that help limit patronage spending. In the first theory, the majority party will realize that it will be out of power at some point and so support reform because there are net economic benefits. In the second case, representatives have an incentive to vote for reform because it will make their state (and all others) better off. Patronage still exists, so these theories must be inadequate.
The reason patronage remains a big part of American politics is that it benefits incumbent representatives. Voters have at least some sense that if they do not re-elect their representatives, their state will suffer because the new representatives will not have the connections to get patronage for the state. Incumbent representatives, which are the only ones that get to vote, have incentives to downplay and vote against patronage reform. This theory explains why politicians make half hearted attempts at reform. Patronage reform is mildly popular, but actually passing reform measures would reduce the election advantage incumbents enjoy, so they make the reform sound good but lack any strong provisions. It also explains why patronage is not completely denied to the minority party. If the minority party were denied all patronage, it would raise the issue to the electorate, which would threaten the whole system.
This theory suggests that a large scale campaign that made people aware of the benefits of eliminating patronage could actually achieve meaningful reform. Though, such a campaign is unlikely because few representatives will support it. I suspect national electoral systems like Proportional Representation or Direct Representation, essentially eliminate patronage, but I am not completely sure why.