Is Central Hudson's first prong a constitutional 'on/off' switch for evaluating commercial speech legality, or a flexible factor?

Under this Court’s four-part Central Hudson framework, truthful speech promoting a commercial transaction is protected under the First Amendment. Since Central Hudson was decided, however, both this Court and the circuit courts have expressed irreconcilable views on how to correctly apply Central Hudson ’s first prong to weigh a transaction’s legality. Only this Court can resolve this split—one growing ever more critical with the emergence of the nation’s medical marijuana industry, a marketplace that operates in compliance with state laws while in violation of federal. The Fifth Circuit, below, adopted a rule under which a moribund and unenforced federal prohibition empowers regulators, at the state level, to censor speech about products that are lawful under state law. If that is correct, then states may adopt virtually any commercial speech bans they desire, so long as there is some law regulating the underlying conduct, even if that law is never enforced. Accordingly, the questions presented are: 1. Is Central Hudson ’s first prong a constitutional “on/off” switch, which treats a product’s legality as a pure threshold question; or is it a flexible and non-dispositive factor among several? 2. Does Central Hudson , or any alternative First Amendment framework the Court might adopt, allow a government to prohibit commercial ii speech about a transaction if it does not actually seek to prohibit the transaction itself?