“Some toxins can be deadly in small doses,” Chief Justice John Roberts wrote last month in the Supreme Court’s opinion in  Buck v. Davis. In Buck, the Supreme Court vacated a death sentence handed down to a black defendant after an “expert” witness told the jury that black defendants are more likely to kill again than whites. Roberts is a terrific writer; his characteristically pithy aphorism rebuked a lower court, which had decided that the “future dangerousness” testimony was “de minimis”—of little importance—and should thus not affect Duane Buck’s death sentence.  (Justices Samuel Alito and Clarence Thomas dissented.)

Curiously, the chief justice was on the other side in a case last week considering an equally grotesque case of racism in criminal justice, Peña-Rodriguez v. Colorado. The court majority struck down a jury verdict thoroughly infused with racism, Roberts joined Alito in his dissent, with Thomas filing a separate one. In Peña-Rodriguez, one racist juror brought into jury deliberations his own opinion (as, he said, “an ex-law enforcement officer”) that a defendant must be guilty of a sex offense “because he’s Mexican and Mexican men take whatever they want.”

The “expert” testimony in Buck took place in open court; the racist talk in Peña-Rodriguez was behind the jury room doors. Jury deliberations are presumed to be secret, and the common law had a rule of “no impeachment,” meaning that jurors could not testify after a verdict that improper considerations had swayed the jury. Over the years, that rule has been codified in state and federal rules of evidence. Federal Rule of Evidence 606(b) is the current federal version—but the rule doesn’t say that jurors can never testify about what went on in the jury room. In fact, juror testimony is permitted to show that 1) the jury was given improper information from outside about the case; 2) someone tampered with the jury with bribes or threats; or 3) someone on the jury just wrote down the wrong verdict on the official form. Colorado’s rule is similar. Neither rule contains an exception for the introduction of racism into deliberations.

That doesn’t mean that any incident of racism is off limits after the fact. If there is evidence from outside the jury (for example, if a court officer overheard racist remarks among jurors), that evidence can be heard. (As a Third Circuit judge, Alito once wrote an opinion in such a jury-racism case; he wrote that testimony from a witness who spoke with a juror outside the jury room was permissible, but not testimony by jurors themselves about what went on inside it.)

The rationale for the “no impeachment” rule is that jurors would not be frank in deliberations if they feared later cross-examination —and that unscrupulous lawyers would harass jurors seeking evidence to reopen a case.

Trial lawyers are intensely curious about what has gone on in the jury room. Often they will approach jurors after the verdict to ask what tipped the case one way or the other. Jurors aren’t required to talk to lawyers, but they are free to.

In Peña-Rodriguez, a Colorado jury found Miguel Angel Pena-Rodriguez guilty of harassing and touching two underage girls in a racetrack women’s room. Pena-Rodriguez said he wasn’t there, but the jury didn’t believe him. After the verdict, though, two jurors gave sworn statements that one juror, identified as “H.C.,” had told fellow jurors that “nine times out of ten Mexican men were guilty of being aggressive toward women and young girls. Citing supposed experience in law enforcement, H.C. added that Mexican men had a “bravado” that led them to sexual abuse.

Following the Colorado rule, the trial court refused to hear the evidence, and the appellate court affirmed the conviction. The Supreme Court granted review to consider whether the Sixth Amendment’s guarantee of an “impartial jury” should, in some cases of alleged racial bias, require an exception to the “no impeachment” rule.

The high court has previously upheld the rule as a protection of the jurors’ rights to deliberate without pressure. In a 1987 case, Tanner v. United States, the court refused to let jurors testify that jurors had regularly gotten drunk at lunch and smuggled pot and cocaine into the courthouse. In a 2014 case called Warger v. Schauers, the court also refused to make an exception for testimony that one juror had lied during jury selection about her personal bias in a case.

The issue in Peña-Rodriguez was whether racism is a different, and more serious, warping influence on a jury. In his majority opinion, Justice Anthony Kennedy wrote that it is. Unlike the intoxication and individual bias in the earlier cases, he said, racism in deliberations is “a familiar and recurring evil that, if left unaddressed, would risk systemic injury to the administration of justice.” It “implicates unique historical, constitutional, and institutional concerns.” Because racism is so powerful and potentially pervasive, a “constitutional rule that racial bias in the justice system must be addressed ... is necessary to prevent a systemic loss of confidence in jury verdicts, a confidence that is a central premise of the Sixth Amendment trial right.”

Thus, Kennedy wrote, the Sixth Amendment supersedes the federal evidence rule.  Trial courts should consider juror testimony that “one or more jurors made statements exhibiting overt racial bias that cast serious doubt on the fairness and impartiality of the jury’s deliberations and resulting verdict.” The trial judge would then have “substantial discretion” to consider whether to order a new trial.

Kennedy noted that a number of states allow juror testimony about racism, and the federal courts of appeals have split on the issue. Though there are “17 jurisdictions that have recognized a racial-bias exception—some for over half a century,” he noted, there have been “no signs of an increase in juror harassment or a loss of juror willingness to engage in searching and candid deliberations.”

An amicus brief filed by the Center on the Administration of Criminal Law at New York University School of Law detailed a study of those jurisdictions. The results suggest that allegations of racism in deliberations are relatively rare—but that when they are made, trial courts take them seriously, often ordering a new trial as a result. “[T]his experience demonstrates that consideration of racial bias does not unduly consume or impair the administration of trials, but that the rule serves an important function in rooting out racial bias,” the brief argues.

Justice Thomas wrote a solo dissent to suggest that Peña-Rodriguez should lose because the “original understanding” of the Sixth Amendment didn’t allow such juror testimony. (My colleague Ken Jost expertly takes down this uncommonly silly argument.)

In the principal dissent, Alito ignored the evidence cited by Kennedy and by the Center, and treated Peña-Rodriguez’s claim as if it were a completely novel and highly threatening innovation in trial practice. “[T]he Court not only pries open the [jury-room] door; it rules that respecting the privacy of the jury room, as our legal system has done for centuries, violates the Constitution.” In fact, the legal system’s “respect” for juror privacy is and has long been distinctly partial. In addition to testifying about jury tampering, jurors in some states have long been able to testify about drug and alcohol use, threats of violence inside the jury room, and even the use of a coin toss to decide a case.

Alito, however, suggested that there is something particularly perilous about posing questions about racism. During oral argument he seemed to suggest that this was another example of political correctness run wild:  “What would happen if one of the jurors has the sensibility of a lot of current college students, and thinks that ...  something that's said in the jury room that falls into one of those categories was a  ... racial comment?”

This concern is, in fact, the reverse of Kennedy’s. The majority writes that because racism is so pervasive and serious a concern, it must be addressed; Alito suggested instead that racism is a kind of endless preoccupation that should be ignored.

I can’t for the life of me figure out how Roberts, as the author of Buck, could join Alito’s opinion in Peña-Rodriguez. Both cases concern explicit racism in official action; while it is sitting, the jury is just as much a part of the state as is the trial court, and thus should be free of racial bias.

The only difference I can see is that in Buck the racism was public, while in Peña-Rodriguez it took place behind closed doors.  That seems a fragile distinction.