Should the government be required to prove proximate cause in addition to but-for causation for the 'death results' enhancement in 21 U.S.C. § 841?

QUESTIONS PRESENTED The questions presented are: I. Should the government be required to prove proximate cause in addition to but-for causation for the “death results” enhancement in 21 U.S.C. § 841? Il. Is the death-or-injury enhancement pursuant to 21 U.S.C. § 841(b)(1)(C) unconstitutionally vague? II. Did the district court judge improperly and inaccurately state the law in its jury instructions when it permitted the jury to utilize the Pinkerton theory of liability to apply the death-or-injury enhancement pursuant to 21 U.S.C. § 841(b)(1)(C)? i