Putting a New Spin on an Existing Machine: Prospects for Polarizing the Fermilab Main Injector

As we continue to explore quantum chromodynamics (QCD) as the theory of the strong force, with gluon interactions in hadrons responsible for more than 98\% of the visible mass in the universe, spin remains an important degree of freedom to be able to manipulate in order to advance the field. In particular, spin-momentum correlations in QCD, broadly analogous to quantum electrodynamical spin-orbit couplings in the hydrogen atom, have risen to the forefront of QCD research over the past decade. The current status of a proposal to polarize the proton beam at the Fermilab Main Injector will be presented, and the physics that could be accomplished with a hadronic fixed-target program at such a facility will be discussed.