With Kahler and the insanity defense, it seems fairly straightforward to see how a Supreme Court decision favorable to the petitioner could affect jurisprudence going forward: states would not have the option of eroding/eliminating the insanity defense.
A decision favorable to the petitioner in Gamble would likewise have constitutional dimensions obvious from its main issue, but it could—perhaps—have more subtle effects as well. One such effect might involve supervised-release-violation proceedings.
As the law currently stands, defendants can (and often do) face both state prosecutions and federal supervised-release revocations for offenses they engage in while serving terms of federal supervised release (after release from prison on earlier federal charges). These dual prosecutions can and do lead to consecutive sentences, with defendants receiving lengthy prison terms for a single offense. For example, a defendant released from federal prison may have a three-year term of supervised release to serve (somewhat similar to parole, though the federal system does not have actual parole). If that defendant sells drugs while on supervised release, they can face prosecution in state court for the new drug charge and they can face revocation of their federal supervised release and another term of federal custody for the supervised-release violation. That federal custody term can be set to run consecutive to the state drug sentence, even though both sentences are for the same drug sale.
With Gamble pending, one may ask: could a decision favorable to the petitioner in Gamble have an effect on these consecutive supervised-release-violation sentences? The issue doesn’t lend itself to straightforward speculation. Jurisprudence on the issue of supervised-release violations suggests that courts could wriggle away from the issue—regardless of the holding that comes down in Gamble—by saying that the supervised-release-violation sentence isn’t really based on a new prosecution doubled up with the state charge. Rather, the theory goes, supervised-release violations relate back to the earlier, original federal charge that gave rise to the supervised-release term, which predated and does not relate to the later drug-sale offense conduct.
The Gamble petition, however, addresses the idea of the separate-sovereigns exception to the Double Jeopardy Clause resting on the vindication of the interests of separate sovereigns. It seems far from sure that Gamble would leave intact the idea that a separate set of prosecutorial interests would insulate consecutive federal supervised-release-violation sentences from attack . . . in the event the High Court does dispense with the separate-sovereigns exception.