Habeas challenge arising from Supreme Court holding narrowing the causation element of the offense can proceed to argument on the question of retroactivity absent explicit retroactivity assertion by the Supreme Court where other circuits have recognized the ruling as retroactive.
http://www.opn.ca6.uscourts.gov/opinions.pdf/18a0165p-06.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.