Michigan v. Long, 463 U.S. 1032, at 1040-1041 (1983), explained when the Court will “weigh in” on a state court matter.  It held,
“When . . . a state court decision fairly appears to rest primarily on federal law, or to be interwoven with the federal law, and when the adequacy and independence of any possible state law ground is not clear from the face of the opinion, we will accept as the most reasonable explanation that the state court decided the case the way it did because it believed that federal law required it to do so. If a state court chooses merely to rely on federal precedents as it would on the precedents of all other jurisdictions, then it need only make clear by a plain statement in its judgment or opinion that the federal cases are being used only for the purpose of guidance, and do not themselves compel the result that the court has reached. In this way, both justice and judicial administration will be greatly improved. If the state court decision indicates clearly and expressly that it is alternatively based on bona fide separate, adequate, and independent grounds, we, of course, will not undertake to review the decision.
This approach obviates [does away with] in most instances the need to examine state law in order to decide the nature of the state court decision, and will at the same time avoid the danger of our rendering advisory opinions. It also avoids the unsatisfactory and intrusive practice of requiring state courts to clarify their decisions to the satisfaction of this Court. We believe that such an approach will provide state judges with a clearer opportunity to develop state jurisprudence unimpeded by federal interference, and yet will preserve the integrity of federal law. ‘It is fundamental that state courts be left free and unfettered by us in interpreting their state constitutions. But it is equally important that ambiguous or obscure adjudications by state courts do not stand as barriers to a determination by this Court of the validity under the federal constitution of state action’ (Citations omitted).”
- Michigan v. Long, 463 U.S. 1032, at 1040-1041 (1983) ↵