Say a state trial court is faced with a federal issue. Say there is a Supreme Court precedent on point. Say, further, there is a mediating opinion by the highest court in the state that, by the trial court’s lights, interprets the Supreme Court precedent incorrectly. Is the state trial court bound, per the doctrine of hierarchical precedent, to follow the mediating opinion, or is it bound, per the supremacy clause, to follow the Supreme Court’s opinion?
Realistically, my gut is that it depends on how obviously the state high court’s opinion is in conflict with the Supreme Court opinion. If the state high court’s interpretation is even minimally “permissible” or “reasonable” then the trial court will feel obliged to follow the state high court’s interpretation. (This seems the only way to give the doctrine of hierarchical stare decisis the bite that it usually enjoys.) If, on the other hand, it is unambiguously contrary to the Supreme Court opinion (the clearest cut case is if it expressly states that the Supreme Court got it wrong) then the trial court will not feel obliged to follow the state high court’s interpretation (and may feel obliged to not follow the state high court’s interpretation).
Note that a trial court will rarely find itself faced with an unambiguous conflict because it has a range of possible moves to reconcile the state high court and Supreme Court opinions. The trial court will have some wiggle room to reinterpret the Supreme Court’s decision; to reinterpret the state high court’s decision; and to characterize the reconciliation in a reasonable-sounding way. (It is an interesting question towards which opinion the trial court should have most fidelity — should it bend over backwards to respect its best interpretation of the Supreme Court’s opinion even if that means embracing a stretched or implausible reinterpretation the state high court’s opinion, vice versa, or neither?)
No cases I have found address this issue, and it appears to be undertheorized in the secondary literature as well.