EAST LANSING, Mich. (AP) — An 1842 U.S. Supreme Court ruling overturning the kidnapping conviction of a white man who seized a Black family and forced them into slavery south of the Mason-Dixon line is still being cited in American jurisprudence, 160 years after enslaved people throughout the U.S. were freed.

Prigg v. Pennsylvania has been cited in 274 other rulings since then, according to the Citing Slavery Project at Michigan State University. They are among more than 7,000 direct citations of slavery-law precedents that continue to guide lawyers and judges, said the project’s director, law professor Justin Simard.

This research into the lasting impact of legal principles related to the ownership of other humans is a counterpoint to efforts by the Trump administration and elected officials in Republican-led states to remove references to America’s racial history and dictate what teachers can discuss in classrooms.

“Because people are invested in trying to pretend that our history of slavery didn’t happen and that its effects are not still with us,” Simard told The Associated Press, “I thought, what better way to prove that slavery had an influence on our legal system than using official legal sources?”

Citations show American jurisprudence is founded on slavery

Most of the slavery precedents concern how property rights were protected by the U.S. Constitution, which was written by wealthy property owners in an era when much of the young nation’s economy was powered by the buying and selling and sweat of enslaved people.

The Supreme Court made slavery’s importance to the America’s founding clear when it ruled that Pennsylvania’s anti-slavery law was an unconstitutional affront to the federal Fugitive Slave Act, and ruled in favor of Edward Prigg, who had forced Margaret Morgan and her children into slavery in Maryland.

The U.S. Constitution clearly granted “to the citizens of the slaveholding states the complete right and title of ownership in their slaves, as property, in every state in the Union, into which they might escape from the state where they were held in servitude,” the court wrote.

The slaveowner’s right to “this species of property” was so fundamental to the framers of the Constitution that without it, “the Union could not have been formed,” the justices added.

Slavery became illegal when the 13th Amendment was adopted in 1865, but Prigg has been most often cited in the decades thereafter, mostly in cases involving property law, as guidance regarding the boundaries between state and federal power, Simard said.

How rulings are still shaped by slavery laws

The continuing use of such citations shows that slavery wasn’t just a historic stain that the 13th Amendment cleaned up — these precedents have an insidious effect on jurisprudence even today, said Leonard Mungo, a Michigan-based civil rights and employment discrimination attorney.

“The unashamed use of human beings as property and as the foundation for the development of jurisprudence regarding property law is the same reason courts across this country rarely find violations of civil rights in employment and other contexts in its rulings and decisions,” Mungo said.

And it’s not like only minorities are affected: Prigg was cited in a 1989 Supreme Court decision overruling most of the $850,000 judgment awarded by a Texas jury to a white football coach who alleged that he was reassigned and demoted from a mostly Black high school because of his race.

Sometimes, slavery precedents are invoked in efforts to reaffirm civil rights. In a 2016 Iowa Supreme Court opinion, dissenting justices said people arrested but not yet formally charged with a crime must be allowed private in-person attorney consultations. Citing how Fugitive Slave Act enforcement shaped the Iowa Constitution, these justices said enslaved people were given the right of counsel — and so should an Iowa man accused of driving under the influence. They were outvoted, 4-3.

‘Digging and digging’

Simard was doing research for his dissertation when he began compiling evidence that northern judges had cited slave cases in the 19th century. He discovered that these citations were more numerous, widespread and recent than he imagined.

“I kept digging and digging and digging and realizing that this wasn’t something just one judge did or some very racist judge or something,” Simard said. “This was just a basic feature of the legal system and it really shocked me, really surprised me.”

More than 12,000 slavery rulings have been identified to date by Simard’s team, which then searches for citations.

And yet many lawyers and judges are either unaware of these origins or don’t think it matters that enslaved humans were the property in question, and consider them “just like regular law,” Simard said. “Not only are we ratifying their treatment as property in the past but also continuing to treat them as property in the present.”

Noting how to move forward

Simard’s team successfully lobbied the editors of The Bluebook, a guide to citations used by the legal profession, to require case notations such as “enslaved party” or “enslaved person at issue.”

“I think just eliminating these cases is impossible,” Simard said. “I think the best approach that lawyers and judges can take is to be thoughtful when they find these cases and cite these cases and to consider whether the law that these cases stand for is still good or not.”

Dylan Penningroth, a professor of law and history at the University of California-Berkeley, agreed.

“These slavery cases are everywhere,” Penningroth said. “How are we ever going to get them all off the book? One answer is you don’t really have to. If lawyers stop relying on these cases, they lose their power.”

Identifying those cases should keep their origins and intents on the minds of judges and litigators, according to Michigan Appeals Court Judge Adrienne Young. She said, “the real harm is in failing to acknowledge the horrific history.”