QUESTION: The Supreme Court's finding that there was an absence of a "plain statement" that federal cases are only used by state courts for the purpose of guidance seems a little problematic. What if state cases do, in fact, include such a plain statement but rely too much on federal cases despite the statement? It seems that there would then be a need for the Supreme Court to review the sincerity/justifiability of the plain statements themselves, which seems like it would only create an additional problem that would waste time and resources. Furthermore, such reviews may open the door to the review of state cases that made an appropriately supported plain statement, which was nevertheless challenged by the state prosecution.
ANSWER: I think that, so long as the state court's plain statement concerning its reliance on state law is facially plausible, the Supreme Court will accept it as genuine. Going beyond that would tangle the Court in a morass, and it seems unlikely the Court (even as a theoretical matter) could ever discern the "true" grounds for another court's decisions. Keep in mind that a state court could rely on many federal decisions to help it understand its own state law.
QUESTION: Has this plain statement idea been useful in practical terms, or has it created more opportunities for he-said-she-said arguments that only weaken the judicial system overall and create more friction between federal and state courts?
ANSWER: This is an interesting empirical question, and I do not know the answer. My sense, though, is that most state courts have, in recent decades, interpreted their constitutions as providing no more protection than the federal constitution, and thus the issue has not arisen. (The increasing visibility of state judicial elections, I think, has contributed to state court judges being a little less defendant-friendly in criminal procedure cases.) You might recall that Proposition 8 -- the first Proposition 8, adopted in the 1980s -- forbids the California Supreme Court from interpreting the California Constitution in a manner that gives criminal defendants greater rights than they enjoy under the federal constitution.
QUESTION: Were Long's arguments unsuccessful alternative pleas? (I am not sure if I used the correct terms there.) Basically, I am wondering why Long was unsuccessful in first arguing that the Fourth Amendment interpretation according to Terry was misapplied and then also arguing that the state constitution would be a better standard than the U.S. Constitution. The Supreme Court's finding seems to be that Long's argument concerning the misapplication of Terry was too much of a reliance on federal law. Why does that part of the finding trump the other argument that Michigan's constitution would be better applied? Is it simply due to Long's failure to cite any state cases that would support his argument for applying the state constitution's standards?
ANSWER: Long was unsuccessful in two respects: (1) preventing the Supreme Court of the United States from reviewing the case on the ground that the Court lacked subject matter jurisdiction, and (2) defending the decision below on the ground that it correctly interpreted the Fourth Amendment. The Michigan Supreme Court's reliance on Terry was only relevant to the first question. Its interpretation and understanding of Terry was relevant to the second question. In hindsight, Long would have been better off urging the Michigan Supreme Court to make abundently clear that its holding rested on state law. But hindsight, as they say, is 20/20. He did not really know this was important until after the Supreme Court's later ruling.