heart of the decision in McGehee v. Casey, 718 F.2d 1137 (D.C.Cir.1983), and was adopted by us in Truong (629 F.2d at 919 n. 10) as we have already observed. In McGehee v. Casey, the court was dealing with a claim of vagueness in the phrase “national security.” It found that the term could be fleshed out by reference to the very Classification Order to which we look in clarifying the term “entitled to receive.” 718 F.2d at 1143-44. We therefore hold that the words “entitled to receive” in the statute in this case can be limited and clarified by the Classification Regulations and, as so limited and clarified, are not vague. United States v. Jolliff, 548 F.Supp. 229, 230 (D.C.Md.1981); United States v. Wilson, 571 F.Supp. 1422, 1426-27 (S.D.N.Y.1983); See Wayne L.Rev., supra at 218.
Turning to the claim of overbreadth, we note at the outset that, unlike the situation presented by a vagueness claim,29 the overbreadth doctrine “is an exception to our traditional rules of practice,” Broadrick v. Oklahoma, 413 U.S. 601, 93 S.Ct. 2908, 37 L.Ed.2d 830 and has not been recognized outside the limited context of the First Amendment. United States v. Salerno, — U.S. -, -, 107 S.Ct. 2095, 2100, 95 L.Ed.2d 697, 707 (1987); Schall v. Martin, 467 U.S. 253, 269, n. 18, 104 S.Ct. 2403, 2412 n. 18, 81 L.Ed.2d 207 (1984); New York v. Ferber, 458 U.S. 747, 767-74, 102 S.Ct. 3348, 3359-63, 73 L.Ed.2d 1113 (1982). So limited, it is “strong medicine,” to be applied “with hesitation and then only as a last resort,” and only if the statute cannot be given a narrowing construction to remove the overbreadth. New York v. Ferber, supra at 769, 102 S.Ct. at 3361. Thus, in McGehee v. Casey, 718 F.2d at 1146, Judge Wald held that “over-breadth analysis should not be deployed when a limiting construction could save the rule from its constitutional defects,” citing Dombrowski v. Pfister, 380 U.S. 479, 491, 85 S.Ct. 1116, 1123, 14 L.Ed.2d 22 (1965), and Cox v. New Hampshire, 312 U.S. 569, 61 S.Ct. 762, 85 L.Ed. 1049 (1941). Moreover, a distinction must be made in this connection between statutes which regulate “conduct in the shadow of the First Amendment” and those which regulate pure speech. The rule makes a distinction “where conduct and not merely speech is involved.” In the conduct context, “over-breadth scrutiny has generally been somewhat less rigid in the context of statutes regulating conduct in the shadow of the First Amendment,” and in such a case “the overbreadth of a statute must not only be real, but substantial as well, judged in relation to the statute’s plainly legitimate sweep.” Broadrick v. Oklahoma, 413 U.S. at 615, 93 S.Ct. at 2918. To be “substantial” in that context, the statute must reach “a substantial number of impermissible applications....” New York v. Ferber, 458 U.S. at 771, 102 S.Ct. at 3362.30
An authority on the scope of the doctrine has formulated a statement of what he characterizes as the three “fundamental circumstances” under which the doctrine may be applied after discussing the foregoing rules. These circumstances are: “(1) when ‘the governmental interest sought to be implemented is too insubstantial, or at least insufficient in relation to the inhibitory effect on first amendment freedoms’; (2) when the means employed bear little relation to the asserted governmental interest; and (3) when the means chosen by the legislature do in fact relate to a substantial governmental interest, but that interest could be achieved by a ‘less drastic means’ —that is, a method less invasive of free speech interests.” Redish, The Warren
29
There is one clear difference between vagueness and overbreadth doctrine: "Overbreadth analysis is perceived as an exception to the rule that an individual is not ordinarily permitted to litigate the rights of third parties; vagueness is not perceived as such an exception." L. Tribe, supra § 12-28, at 719-20. This, however, is not an invariable rule but one whose application depends on the facts of each case. McGehee v. Casey, 718 F.2d at 1146.
30
The “upshot” of Ferber and cases subsequent to it, as Professor Tribe puts it, "is a mounting burden on the individual to show that the apparent inhibition of protected expression [in the statute under review] is in fact highly probable and socially significant.” L. Tribe, American Constitutional Law, supra, § 12-25, at 714.