James Buchanan was one of the founding fathers of public choice theory, along with Gordon Tullock and some others (Bill Niskanen, Mancur Olson, et al). Public choice, despite the obscure name, is quite simple. It says that market behavior does not end where government begins. Politicians and other government actors are not angels. They are just as self-interested as you or I. Public choices are subject to the same incentives as private choices.
Buchanan’s simple, powerful insight won him the economics Nobel in 1986. Don Boudreaux made some brief remarks at Buchanan’s recent 90th birthday celebration. They’re worth reading, especially if you aren’t familiar with Buchanan and his very distinguished place in the history of economic thought. Also worth reading is his Nobel lecture.