  We calculate high-precision constraints on Natural Inflation relative to
current observational constraints from Planck 2018 + BICEP/Keck(BK15)
Polarization + BAO on $r$ and $n_S$, including post-inflationary history of the
universe. We find that, for conventional post-inflationary dynamics, Natural
Inflation with a cosine potential is disfavored at greater than 95\% confidence
out by current data. If we assume protracted reheating characterized by
$\overline{w}>1/3,$ Natural Inflation can be brought into agreement with
current observational constraints. However, bringing unmodified Natural
Inflation into the 68\% confidence region requires values of $T_{\mathrm{re}}$
below the scale of electroweak symmetry breaking. The addition of a SHOES prior
on the Hubble Constant $H_0$ only worsens the fit.
