  In Wyeth v. Levine the Supreme Court once again failed to reconcile the
interpretive presumption against preemption with the sometimes competing
Chevron doctrine of deference to agencies' reasonable statutory
interpretations. Rather than resolve the issue of which principle should govern
where the two principles point toward opposite results, the Court continued its
recent practice of applying both principles halfheartedly, carving exceptions,
and giving neither its proper weight.
  This analysis situates Wyeth within the larger framework of the Court's
recent preemption decisions in an effort to explain the Court's hesitancy to
resolve the conflict. The analysis concludes that the Court, motivated by its
strong respect for congressional intent and concern to protect federalism,
applies both the presumption against preemption and the Chevron doctrine on a
sliding scale. Where congressional intent to preempt is clear and vague only as
to scope, the Court is usually quite deferential to agency determinations, but
where congressional preemptive intent is unclear, agency views are accorded
less weight.
  The Court's variable approach to deference is defensible as necessary to
prevent unauthorized incursion into areas of traditional state sovereignty, but
its inherent unpredictability sows confusion among regulated parties, and the
need for flexibility prevents the Court from adopting any of the more
predictable across-the-board approaches to deference proposed by the Court's
critics. A superior approach would combine the Court's concern for federalism
with the certainty of a bright-line rule by granting deference to agency views
where Congress has spoken via a preemption clause of ambiguous scope and no
deference where Congress has remained silent.
