  Polstar is a proposed NASA MIDEX space telescope that will provide
high-resolution, simultaneous full-Stokes spectropolarimetry in the far
ultraviolet, together with low-resolution linear polarimetry in the near
ultraviolet. This observatory offers unprecedented capabilities to obtain
unique information on the magnetic and plasma properties of the magnetospheres
of hot stars. We describe an observing program making use of the known
population of magnetic hot stars to test the fundamental hypothesis that
magnetospheres should act to rapidly drain angular momentum, thereby spinning
the star down, whilst simultaneously reducing the net mass-loss rate. Both
effects are expected to lead to dramatic differences in the evolution of
magnetic vs. non-magnetic stars.
