  We present simultaneous observations by EUVE, ASCA, and RXTE of the type~1
Seyfert galaxy NGC 5548. These data indicate that variations in the EUV
emission (at $\sim 0.2 $keV) appear to lead similar modulations in higher
energy ($\ga 1 $keV) X-rays by $\sim$10--30 ks. This is contrary to popular
models which attribute the correlated variability of the EUV, UV and optical
emission in type~1 Seyferts to reprocessing of higher energy radiation. This
behavior instead suggests that the variability of the optical through EUV
emission is an important driver for the variability of the harder X-rays which
are likely produced by thermal Comptonization. We also investigate the spectral
characteristics of the fluorescent iron K$\alpha$ line and Compton reflection
emission. In contrast to prior measurements of these spectral features, we find
that the iron K$\alpha$ line has a relatively small equivalent width
($W_{K\alpha} \sim 100 $eV) and that the reflection component is consistent
with a covering factor which is significantly less than unity ($\Omega/2\pi
\sim 0.4$--0.5). Notably, although the 2--10 keV X-ray flux varies by $\sim \pm
25$% and the derived reflection fraction appears to be constant throughout our
observations, the flux in the Fe~K$\alpha$ line is also constant. This behavior
is difficult to reconcile in the context of standard Compton reflection models.
