One of the hallmarks of Justice Kennedy’s jurisprudence has been something I dubbed “substantive federalism.” This is the notion that states conferring liberty, or dignity as he calls it, on its people should inform the federal constitutional inquiry. We saw this in Lawrence, when Justice Kennedy noted all of the states that abolished sodomy laws as evidence that Texas’s law cannot stand. We saw this in Windsor, where Justice Kennedy noted the (few) states that have conferred the dignity of marriage on same-sex couples in recent years (this number was much smaller than the number of states in Lawrence). I’m sure in whatever opinion we see recognizing a right to same-sex marriage, Justice Kennedy will point out all of the states that legalized gay marriage following Windsor (to say nothing of the undefeated winning streak in the federal courts of invalidating other laws).

But, this analysis discounts all of the states that banned gay marriage in the same period (a much larger number). Why? Because substantive federalism is a one-way ratchet to promote liberty (at least in the libertarian eyes of AMK). Rather than hewing to Justice Brandeis’s famous “laboratories of democracy,” model, Justice Kennedy adheres to a “laboratories of liberty” model. When states confer liberty on people that promotes liberty, that informs the federal constitutional inquiry. When states deprive people of that dignity (such as by banning gay marriage), those democratic choices are contrary to the liberty required by the constitution. (My summer writing project will explain this topic in some detail).

We also see similar moves in Justice Kennedy’s 8th Amendment jurisprudence. The entire “national consensus” model, relied on in Atkins, Roper, and Kennedy v. Louisiana, all look to the states to track evolving standards of decency, and inform what liberty demands under the 8th Amendment. His opinion in Hall v. Florida continues that trend of substantive federalism in the laboratories of liberty.

Asides from his reliance on professional associations, the crux of the majority opinion focused on what states are, and are not doing, and how these varying treatments inform the 8th Amendment.

First, AMK discusses the role the states play in informing the 8th Amendment:

Kennedy’s focus on the states sees them not as laboratories of democracy. It’s not enough that the states experiment–which is precisely what Atkins invited them to do. Instead, they must promote more liberal policies, to make it tougher to executive someone with an “intellectual disability” (the condition formerly known as “mental retardation”).

The states that are laboratories of liberties get gold constitutional stars.

A significant majority of States implement the protec­ tions of Atkins by taking the SEM into account, thus acknowledging the error inherent in using a test score without necessary adjustment. This calculation provides “objective indicia of society’s standards” in the context of the Eighth Amendment. Roper, 543 U. S., at 563.

Only the Kentucky and Virginia Legislatures have adopted a fixed score cutoff identical to Florida’s. Ky. Rev. Stat. Ann. §532.130(2) (Lexis Supp. 2013); Bowling v. Com- monwealth, 163 S. W. 3d 361, 375 (Ky. 2005); Va. Code Ann. §19.2–264.3:1.1 (Lexis Supp. 2013); Johnson v. Commonwealth, 267 Va. 53, 75, 591 S. E. 2d 47, 59 (2004), vacated and remanded on other grounds, 544 U. S. 901 (2005). Alabama also may use a strict IQ score cutoff at 70, although not as a result of legislative action . . . . In addition to these States, Arizona, Delaware, Kansas, North Carolina, and Washington have statutes which could be interpreted to provide a bright-line cutoff leading to the same result that Florida mandates in its cases.

Thus, at most nine States mandate a strict IQ score cutoff at 70. Of these, four States (Delaware, Kansas, North Carolina, and Washington) appear not to have considered the issue in their courts. On the other side of the ledger stand the 18 States that have abolished the death penalty, either in full or for new offenses, and Ore­ gon, which has suspended the death penalty and executed only two individuals in the past 40 years. See Roper, 543 U. S., at 574 (“[The] Court should have considered those States that had abandoned the death penalty altogether as part of the consensus against the juvenile death penalty”). In those States, of course, a person in Hall’s position could not be executed even without a finding of intellectual disability. Thus in 41 States an individual in Hall’s position—an individual with an IQ score of 71—would not be deemed automatically eligible for the death penalty.

In addition to merely counting states, Justice Kennedy measures the “direction of change.” This has shades of his trending analysis in Lawrence, of states that have abolished sodomy bans, and in Windsor, of states that have conferred the dignity of same-sex marriage.

These aggregate numbers are not the only considera­ tions bearing on a determination of consensus. Consistency of the direction of change is also relevant. See id., at 565–566 (quoting Atkins, supra, at 315). Since Atkins, many States have passed legislation to comply with the constitutional requirement that persons with intellectual disability not be executed. Two of these States, Virginia and Delaware, appear to set a strict cutoff at 70, although as discussed, Delaware’s courts have yet to interpret the law. In contrast, at least 11 States have either abolished the death penalty or passed legislation allowing defend­ ants to present additional evidence of intellectual disabil­ ity when their IQ test score is above 70.

This “consistency in the trend” can only point in one direction–towards more liberal ends.

In summary, every state legislature to have considered the issue after Atkins—save Virginia’s—and whose law has been interpreted by its courts has taken a position contrary to that of Florida … The rejection of the strict 70 cutoff in the vast majority of States and the “consistency in the trend,” Roper, supra, at 567, toward recognizing the SEM provide strong evi­ dence of consensus that our society does not regard this strict cutoff as proper or humane.

AMK attempts to distinguish this case from Atkins, and makes the point abundantly clear that states cannot experiment without discretion. And ultimately, that discretion is cabined by Justice Kennedy sense of propriety.

In Atkins, the Court stated:

“Not all people who claim to be mentally retarded will be so impaired as to fall within the range of mentally retarded offenders about whom there is a national consensus. As was our approach in Ford v. Wainwright with regard to insanity, ‘we leave to the State[s] the task of developing appropriate ways to en­ force the constitutional restriction upon [their] execu­ tion of sentences.’ ” 536 U. S., at 317 (quoting Ford v. Wainwright, 477 U. S. 399, 416–417 (1986); citation omitted).

As discussed above, the States play a critical role in ad­ vancing protections and providing the Court with infor­ mation that contributes to an understanding of how intel­ lectual disability should be measured and assessed. But Atkins did not give the States unfettered discretion to define the full scope of the constitutional protection.

…

Further­ more, immediately after the Court declared that it left “‘to the States the task of developing appropriate ways to enforce the constitutional restriction,’” id., at 317, the Court stated in an accompanying footnote that “[t]he [state] statutory definitions of mental retardation are not identical, but generally conform to the clinical definitions,” ibid.

Thus Atkins itself not only cited clinical definitions for intellectual disability but also noted that the States’ standards, on which the Court based its own conclusion, conformed to those definitions.