  We explore the effects of a heavy fermion doublet in a simplified version of
the standard electroweak theory. We integrate out the doublet and compute the
exact effective energy functional of spatially varying gauge and Higgs fields.
We perform a variational search for a local minimum of the effective energy and
do not find evidence for a soliton carrying the quantum numbers of the
decoupled fermion doublet. The fermion vacuum polarization energy offsets the
gain in binding energy previously argued to be sufficient to stabilize a
fermionic soliton. The existence of such a soliton would have been a natural
way to maintain anomaly cancellation at the level of the states. We also see
that the sphaleron energy is significantly increased due to the quantum
corrections of the heavy doublet. We find that when the doublet is slightly
heavier than the quantum--corrected sphaleron, its decay is exponentially
suppressed owing to a new barrier. This barrier exists only for an intermediate
range of fermion masses, and a heavy enough doublet is indeed unstable.
