The Supreme Court in Lopez v. Gonzales, Docket No. 05-547 (S.Ct. Dec. 5, 2006), held that a conviction for simple possession of a controlled substance did not qualify as an aggravated felony under the Immigration and Naturalization Act, even if punishable as a felony under state law. The Court construed the statute, 8 U.S.C. 1101(a)(43)(B), as requiring the predicate drug conviction to be punishable as a felony under the federal Controlled Substances Act. Since the CSA punishes simple possession as a misdemeanor, such a conviction is not a "felony punishable under the [CSA]" and hence not a "drug trafficking crime". Additionally, the Court noted that construing "trafficking" as including simple possession created "incoherence wiht any commonsense conception of 'illicit trafficking,' the term ultimately being defined." "Trafficking" usually means some sort of commercial dealing, according to the Court, and commerce had not part in the Petitioner's prior conviction for helping someone else to possess drugs. Thomas dissented.
For additional discussion, Steve Sady has an excellent entry in the Ninth Circuit Blog, located here.