Can a federal conviction obtained in violation of the Constitution be challenged in federal habeas corpus?

Before section 2255 was enacted in 1948, a federal conviction obtained in violation of the Constitution could be challenged in federal habeas corpus. See Fay v. Noia, 372 U.S. 391, 409, 83 S.Ct. 822, 9 L.Ed.2d 837. A section 2255 motion is the counterpart of habeas corpus.³ It would seem to follow that the same relief should be available to a federal prisoner under such a motion as is now available to a state prisoner under habeas corpus, or as would be now available to a federal prisoner but for the enactment of section 2255.⁴