  Measurements of deuterium in the local interstellar medium have revealed
large variations in D/H along different lines of sight. Moreover, recent {\it
Far Ultraviolet Spectroscopic Explorer} (FUSE) measurements find D/H to be
anticorrelated with several indicators of dust formation and survival,
suggesting that interstellar deuterium suffers significant depletion onto dust
grains. This in turn implies that the total deuterium abundance in the local
Galactic disk could be as high as $\sim 84 %$ of the primordial D abundance. It
was proposed that the infall/accretion of pristine gas is needed to explain
such a high deuterium abundance. However, we point out that the infall needed
to maintain a high present-day D/H is, within the preferred models, in tension
with observations that gas represents only some $\sim 20%$ of Galactic baryons,
with the balance in stars. We study this tension in the context of a wide class
of Galactic evolution models for baryonic processing through stars, which show
that deuterium destruction is strongly and cleanly correlated with the drop in
the gas fraction. We find that FUSE deuterium observations and Galactic gas
fraction estimates can be reconciled in some models; these demand a significant
infall rate of pristine material that almost completely balances the rate of
star formation. These successful models also require that the average fraction
of gas that is returned by dying stars is less than 40% of the initial stellar
mass. Cosmological implications of dust depletion of D in high-redshift systems
are discussed.
