  AR Scorpii (AR Sco) is a binary star system containing the only known white
dwarf (WD) pulsar. Previously reported photometric datasets only provide
coverage back to 2005, but we extend the observational baseline for AR Sco back
to the beginning of the 20th century by analyzing observations from the Digital
Access to a Sky Century at Harvard project (DASCH). We find that the orbital
waveform of AR Sco remained constant across that baseline with no significant
deviations from its average brightness. This result strongly suggests that the
absence of accretion in modern observations is a long-term feature of AR Sco.
Additionally, the DASCH light curve provides an opportunity to test an earlier
prediction that an obliquity of the WD would result in a precessional period
observable in long-term studies of the orbital light curve. The DASCH
observations do not indicate the presence of such a period, and we show that
previous, inconclusive tests of this hypothesis were insensitive to the
existence of a precessional period. Furthermore, the long DASCH baseline
enables us to constrain the rate of change of the orbital frequency to
$\dot{\nu} \lesssim 3.8\times10^{-20}$ Hz s$^{-1}$, constraining the efficacy
of magnetic braking as a mechanism of angular-momentum loss in this system.
Finally, we discuss how the combination of the orbital waveform's stability,
high amplitude, and short period should make it possible to identify additional
WD pulsars in all-sky survey data.
