concurring:
I concur wholeheartedly in the majority’s opinion. I write separately only to emphasize that nothing in this opinion diminishes the right of a federal defendant to challenge his sentence by means of a 28 U.S.C. § 2255 petition if the conviction forming the predicate for enhancement is subsequently reversed or vacated in a collateral proceeding, as long as that collateral proceeding was commenced prior to the date the federal sentence was imposed. Cf. Johnson v. Mississippi, 486 U.S. 578, 108 S.Ct. 1981, 100 L.Ed.2d 575 (1988).