It's tricky politically, because there's a big difference in interest: rural areas and states who are net recipients of the subsidies are generally strongly in favor, whereas urban areas who are the net payers are generally indifferent. You might lose a primary or election in Iowa over farm subsidies, but it's never in the top 10 issues on anyone's mind in an election in NYC, Atlanta, or SF.<p>That and the coalitions line up weirdly. The Republicans are usually the initators of cut-government-spending types of bills, but there are a lot of rural and farm-state "heartland" Republicans who support the programs, so it tends to be a nonstarter within the caucus. Democrats tilt more heavily urban, but the rural Democrats wield fairly strong influence, partly because Democrats feel it's important to keep their relatively meagre rural inroads (so folks like Kent Conrad in ND and Ben Nelson in NE get outsized influence). And the urban Democrats usually have other things they want to spend their political capital on: "I successfully cut farm subsidies" is going to get you a disinterested yawn in most urban Democratic districts.
If you think this is bad you should take a look at the EU Common Agricultural Policy which represents almost half the EU's entire budget.<p><a href="http://en.wikipedia.org/wiki/Common_Agricultural_Policy" rel="nofollow">http://en.wikipedia.org/wiki/Common_Agricultural_Policy</a>
Dead men farming - circa 1842: <a href="http://www.gutenberg.org/files/1081/1081-h/1081-h.htm" rel="nofollow">http://www.gutenberg.org/files/1081/1081-h/1081-h.htm</a>