Tactically, eliminating food stamps through a farm subsidies "bumper shot" would be brilliant, but not really necessary. The attack on the subsidies is a symbolic shout-out to Bush's conservative base, the CATO's and Stephen Moore's of the world. To let that die while simultaneously kidney-punching the poor would win neither the President nor the party any friends, and let's not forget a farm industry plenty able to support Democrats in the '06 midterms. If Bush is taking them on, my hunch is he's doing it for real. And if he loses, food stamps is one of those programs with sacrosanct symbolism, retaining a facade of compassionate conservatism has been important to this bunch and I can't see them sacrificing it for such slight budgetary gain.
