  SHORTENED ABSTRACT: We present numerical investigations designed to
critically test models of the origin of the Magellanic Stream. The most
developed model is the tidal model which fails to reproduce several of its
characteristic properties. We suggest an alternative model for the origin of
the Stream which can explain all of its observed features and dynamics, as well
as provide a strong constraint on the distribution of gas within the halo of
the Milky Way. We propose that the Stream consists of material which was
ram-pressure stripped from the Magellanic System during its last passage
through an extended ionized disk of the Galaxy. This collision took place some
500 million years ago at a galacto-centric distance of about 65 kpc, and swept
$\sim 20$\% of the least bound HI into the Stream. The gas with the lowest
column density lost the most orbital angular momentum, and is presently at the
tip of the Stream, having fallen to a distance of $\sim 20$ kpc from the Milky
Way attaining a negative velocity of 200 \kms. To prevent the stripped material
from leading the Magellanic Clouds and attaining too large an infall velocity,
we postulate the existence of an extended dilute halo of diffuse ionized gas
surrounding the Milky Way. If the halo gas is at the virial temperature of the
potential well of the Milky Way, its thermal emission would contribute $\sim$
40\% of the observed diffuse background radiation in the 0.5-1.0 keV (M) band,
consistent with recent ROSAT measurements as well as pulsar dispersion
measures. Ram pressure stripping
