You need to read the opinion in United States v. Blewett, 12-5226, 12-5582 (6th Cir. May 17, 2013)(found here). Both the majority and the dissent are beautifully written. The majority cites Yick Wo v. Hopkins, 118 U.S. 356 (1886)* AND Justice Scalia's writings on statutory interpretation. How often do you see that?
The cousins Blewett were sentenced in 2005 to 10-year mandatory minimum sentences under the old crack law. They sought retroactive resentencing under 18 U.S.C. 3582(c)(2) and 28 U.S.C. 994(u). They argued that because the guidelines are driven by the mandatory minimum sentences set by Congress, the mandatory structure is an integral part of the guideline. New mandatory minimums are not solely statutory, but also part of the retroactive guideline. Thus the ability to file under 3582(c).
Judges Merritt and Martin agreed with the Blewetts, but added an Equal Protection angle to the argument. It makes for powerful reading. Judge Merritt ruled "that the federal judicial perpetuation of the racially discriminatory mandatory minimum crack sentences for those defendants sentenced under the old crack sentencing law... would violate the Equal Protection Clause." "Like slavery and Jim Crow laws, the intentional maintenance of discriminatory sentences is a denial of equal protection."
Judge Gilman dissented. He reasoned since Equal Protection was not argued or briefed by the Blewetts or the government, it should not form the basis for an opinion. He also felt the majority opinion ran counter to statutes and current case law.
* Yick Wo is a case out of San Francisco where a facially nondiscriminatory zoning law was used to put Chinese laundries - and only laundries run by those of Chinese descent - out of business. The Supreme Court found it in violation of the Constitution as applied. Yes, I had to look it up. Very interesting reading. You can read it here for free.