This post has been updated.

In late 1972, while drafting the Supreme Court’s landmark Roe v. Wade decision legalizing abortion, Justice Harry Blackmun asked fellow justice William J. Brennan Jr. to review a section in the opinion concerning the Roman Catholic Church.

“Your judgment as to this will be most helpful,” Blackmun wrote, according to a biography of Brennan.

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Blackmun turned to Brennan for precise clarification of the church’s position on abortion vehemently opposed to it — because he expected his colleague would know it by heart. Brennan was the court’s lone Catholic. And he was on Blackmun’s side of history — to legalize abortion, the church’s position be damned.

The story of Brennan’s seminal role in legalizing abortion had been largely overlooked as President Trump considered two Catholic judges, Brett M. Kavanaugh and Amy Coney Barrett, as potential nominees to fill the seat being vacated by Justice Anthony M. Kennedy, considered a pivotal swing vote.

In selecting Kavanaugh on Monday night, Trump chose a judge reared in Washington’s finest Jesuit institutions, including Georgetown Preparatory School. Kavanaugh, who serves on the U.S. Court of Appeals for the D.C. Circuit, is active in several Catholic organizations in the area. Trump pointed out that he coaches his daughter’s Catholic Youth Organization basketball team.

During his brief remarks, Kavanaugh referenced his faith in God, but largely avoided any deeper discussion of his religious beliefs — probably knowing the subject will come up during his confirmation hearing, just as it did for Brennan six decades ago.

Brennan’s pivotal role in legalizing abortion — persuading Blackmun and other justices to view it as a privacy issue — might prove particularly instructive, given Trump’s campaign pledge to appoint justices who will overturn Roe. Given the current court makeup, one vote could flip the law on one of the country’s most divisive issues.

The court is now dominated by Catholics, with Kennedy, Chief Justice John G. Roberts Jr. and Justices Clarence Thomas, Sonia Sotomayor, Samuel A. Alito Jr. and Neil M. Gorsuch being raised in the church. But when President Dwight D. Eisenhower appointed Brennan in 1956, Protestants vastly outnumbered Catholics on the court.

The six Catholics on the court before Brennan included Roger B. Taney, who authored the decision in Dred Scott v. Sandford, which held that those of African descent could not be U.S. citizens. Many historians consider the ruling in Dred Scott to be the court’s worst decision.

After the court ruled in Roe, some prominent Catholics compared the decision to Dred Scott. Some even called for Brennan to be excommunicated. In their biography of Brennan, Seth Stern and Stephen Wermiel wrote that the justice was “saddened to be singled out by members of his church.”

Nobody should have been too surprised that he bucked canon law.

Eisenhower appointed Brennan during his reelection campaign in 1956. The Republican president and his political advisers thought that Brennan, a Catholic Democrat from New Jersey, would appeal to voters across the aisle, then lean conservative as a Catholic on the bench. A political twofer.

Brennan’s appointment occurred when Congress was in recess, meaning he didn’t need to be confirmed by the Senate. After Eisenhower won, he renominated Brennan, subjecting the justice to a confirmation hearing. Brennan’s religion became a key issue, with some senators inquiring about how he could rule on constitutional issues while also maintaining allegiance to the pope and the Roman Catholic Church “on all matters of faith and morals.”

This is how Brennan answered one senator:

Senator, I think the oath that I took is the same one that you and all of the Congress, every member of the executive department up and down all levels of government take to support the Constitution and laws of the United States. I took that oath just as unreservedly as I know you did, and every member and everyone else of our faith in whatever office elected or appointive he may hold. And I say not that I recognize that there is any obligation superior to that, rather that there isn’t any obligation of our faith superior to that. And my answer to the question is categorically that in everything I have ever done, in every office I have held in my life or that I shall ever do in the future, what shall control me is the oath that I took to support the Constitution and laws of the United States and so act upon the cases that come before me for decision that it is that oath and that alone which governs . . .

Brennan was confirmed. He served 34 terms, becoming one of the court’s most famous liberal stalwarts. In recounting the mistakes of his presidency, Eisenhower is said by some historians to have listed Brennan — though, as Wermiel pointed out in a law review article, no one has ever confirmed that Eisenhower made such a remark.

Still, Brennan is often used as an example of how Supreme Court nominees sometimes don’t pan out as expected.

Or did he?

Wasn’t he precisely the person he described himself to be during his confirmation hearing?

The biography by Stern and Wermiel, which drew heavily on interviews with Brennan, is illuminating on these questions. It turns out that Brennan was fundamentally and morally opposed to abortion. You read that correctly: The justice who helped persuade a majority of the court to legalize abortion found the practice unthinkable — personally, but not constitutionally.

“I wouldn’t under any circumstances condone an abortion in my private life,” he told the authors. “But that has nothing to do with whether or not those who have different views are entitled to have them and are entitled to be protected in their exercise of them. That’s my job in applying and interpreting the Constitution.”

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