A new study by the Cato Institute confirms what you may have already suspected:  Many more prosecutors than criminal defense attorneys go on to become federal judges.

In recent years, there's been a fair amount of discussion about the lack of ethnic and gender diversity on the federal bench. But as Cato's Clark Neily points out, lack of professional diversity is problematic as well.

Yes, yes, judges take an oath to be impartial and faithfully apply the law—but that doesn't mean biases based on background experience don't still creep in.

Neily offers an analogy. Imagine, he writes, "you're a diehard Ohio State football fan, and every time the Buckeyes play the Wolverines, three or four of the seven referees on the field are Michigan alums, while only one is an Ohio State alum. You'd most likely prefer a more balanced officiating crew because even though referees are required to be neutral, there are many close calls in football, and it's reasonable to suppose that even the most conscientious referee might tend to shade those calls in favor of his alma mater."

And sometimes, those close calls are what decide the game.

So just how lopsided is the federal judiciary?

Cato researchers examined the professional background of every sitting Article III federal judge and assigned them numeric codes based on six categories: criminal prosecutor, civil prosecutor, nonlitigating government lawyer (e.g., agency general counsel), civil liberties litigator (e.g., ACLU, Institute for Justice, etc.), non-public criminal defense attorney and public defender. (Those who had no experience in any of the categories were labeled "other" and not assigned a numeric code for the analysis. Judges with experience in more than one category got double-counted.)

Cato found that former criminal prosecutors outnumber former criminal defense attorneys by a ratio of four to one. If you expand the group to include those who formerly advocated for the government in both civil and criminal cases versus those who advocated against, the disparity is seven to one.

The imbalance is probably irrelevant for the bulk of cases that make up the federal docket—disputes between private parties. But according to the Administrative Office of the U.S. Courts, about 20% of all federal cases are criminal prosecutions, and another 15% involve challenges to government power, such as civil rights cases or habeas petitions. And in those cases, concerns about potential bias are understandable.

As Neily writes, it's "perfectly reasonable for an Ohio State fan to balk at the prospect of an officiating crew consisting mostly of Michigan alums, just as it is perfectly reasonable for a criminal defendant to be leery of a federal bench on which former prosecutors outnumber former criminal defense attorneys four to one."

One thing the Cato study doesn't dig into is why—what's behind the imbalance?

One reason may be an unfortunate tendency to conflate defense counsel with their clients. 

Consider what happened in 2016, when U.S. Court of Appeals for the Eighth Circuit Judge Jane Kelly—a former public defender—was floated as a possible Supreme Court pick before President Obama (unsuccessfully) nominated Merrick Garland. 

The conservative Judicial Crisis Network ran an attack ad blasting Kelly for defending "an admitted child molester… That client was found with more than 1,000 files of child pornography and later convicted for murdering and molesting a 5-year-old girl from Iowa."

"Jane Kelly doesn't belong on the Supreme Court," stated the ad, which wrongly attributed to Kelly a statement by a psychologist that the man was not a threat to society.

You might also recall Hillary Clinton was excoriated in some quarters for her representation as a young lawyer of a man accused of raping a child—never mind that she didn't seek the work, but was appointed by a judge. 

Likewise, her running mate Tim Kaine was attacked in a television ad for his work as a criminal defense lawyer. "Tim Kaine. He has a passion for defending the wrong people," the Republican National Committee ad stated.

Trump picks have also faced heat for the clients they represented. For example, before Kirkland & Ellis white-collar defense partner Brian Benczkowski was confirmed as head of DOJ's criminal division, he was criticized for representing a Russian bank.

"The decision to take on such a controversial Russian client raises questions about Benczkowski's judgment," The Washington Post opined.

It's surprising to me how often people don't separate the lawyer from the client—how easy they find it to forget that our adversarial judicial system is premised on the notion that even bad guys get lawyers, but that doesn't make the lawyers bad.