Is applying the wrong causation standard when upwardly departing under the sentencing guidelines or upwardly varying under the statutory sentencing factors pursuant to 18 U.S.C. § 3553 for the death of a person who consumed fentanyl ever harmless error?

QUESTIONS PRESENTED 1, Is applying the wrong causation standard when upwardly departing under the sentencing guidelines or upwardly varying under the statutory sentencing factors pursuant to 18 U.S.C. § 3553 for the death of a person who consumed fentanyl ever harmless error? 2. Must the Government prove strict but for causation when death resulted to justify a sentence of a term of imprisonment more than four times the high end of the calculated guideline range for the offense? 1