  Precision neutrino oscillation experiments of the future---of which DUNE is a
prime example---require reliable event generator tools. The 1--4 GeV energy
regime, in which DUNE will operate, is marked by the transition from the
low-energy nuclear physics domain to that of perturbative QCD, resulting in
rich and highly complex physics. Given this complexity, it is important to
establish a validation procedure capable of disentangling the physical
processes and testing each of them individually. Here, we demonstrate the
utility of this approach by benchmarking the GENIE generator, currently used by
all Fermilab-based experiments, against a broad set of inclusive
electron-scattering data. This comparison takes advantage of the fact that,
while electron-nucleus and neutrino-nucleus processes share a lot of common
physics, electron scattering gives one access to precisely known beam energies
and scattering kinematics. Exploring the kinematic parameter range relevant to
DUNE in this manner, we observe patterns of large discrepancies between the
generator and data. These discrepancies are most prominent in the
pion-producing regimes and are present not only in medium-sized nuclei,
including argon, but also in deuterium and hydrogen targets, indicating
mismodeled hadronic physics. Several directions for possible improvement are
discussed.
