This week, when the U.S. Supreme Court hears oral arguments for a Missouri religious discrimination case that could sweep aside legal obstacles to school voucher programs, Justice Neil Gorsuch will be on the bench.

Gorsuch, President Donald Trump’s first nominee to the ideologically divided court, may well cast the deciding vote in the case, Trinity Lutheran Church of Columbia, Inc. v. Comer. That fact makes his long-awaited arrival a watershed moment for Catholics concerned about the court’s direction on religious freedom, life and family issues.

Gorsuch didn’t get on Trump’s short list of Supreme Court candidates by chance. According to insiders on both sides of the partisan divide, Gorsuch owes his nomination, at least in part, to Leonard Leo, the 51-year-old Catholic executive vice president of The Federalist Society — a conservative organization that calls for judges to interpret the constitution according to the Founders’ original intent.

According to a profile in The New Yorker, Leo first received an invitation to meet with Trump last spring, as the real estate mogul was gaining ground on his GOP rivals in the primaries.

Trump told Leo, “People don’t know who I am on these issues, and I want to give people a sense of that.”

Leo responded, “That’s a great idea—you’re creating a brand.”

As Leo tells it, Trump wanted a respected pro-life candidate who was not “weak,” and would “interpret the Constitution the way the Framers meant it to be.”

When Trump effectively secured the GOP nomination, Leo began compiling a list of candidates, and by mid-May 2016, Trump presented that list to the party faithful.

In the early fall, a second list was released, and Gorsuch’s name was included.

When Trump turned to Leo for help with his first nominee to the high court, he was soliciting the advice of a devout pro-life Catholic and a graduate of Cornell Law School, who had spent much of his career at The Federalist Society, where he helped promising conservative lawyers solidify their judicial philosophy and secure appointments to the federal bench.

“Leo’s life has been shaped as much by Catholicism as by conservatism,” notes the liberal author of the New Yorker article, Jeffrey Toobin, who occasionally expresses his antagonism toward Leo’s values, but offers a compelling portrait of his religious and family background:

In 1992, (Leo and his wife) had their first child, Margaret, who was born with spina bifida, which confined her to a wheelchair and led to other medical complications. ‘She was a real miracle, despite having a really serious handicap, and many other issues, too,’ Leo said. ‘She was extraordinarily vivacious, talented, simple. She had a great way with people.’ Clarence Thomas, Leo said, still keeps her drawings under glass on his desk. Margaret’s example deepened Leo’s Catholic faith. She encouraged him to go to daily Mass, though he found keeping up attendance difficult. During a family vacation in 2007, when Margaret was fourteen, Leonard promised her that he would resume the practice. On the morning after they returned, Leo got up early to go to Mass. He looked in on Margaret. Then, as he was walking down the hall, she started gasping for breath. She died shortly afterward. ‘I will always think that she did her job.’ The Leos have six other children, including an eight-year-old son who also has spina bifida. A friend of Leo’s said, ‘Leonard comes to his pro-life views out of a place of incredible sincerity. They always treated Margaret throughout her life like any other child.’ According to Leo, the vast majority of abortions are a consequence of voluntary, consensual sexual encounters, an opinion that influences his view of the procedure.’ We can have a debate about abortion,” he told me. “It’s a very simple one for me. It’s an act of force. It’s a threat to human life. It’s just that simple."

Immediately after Trump’s upset election victory, Leo began meeting with potential nominees for the high court, and honed in on their judicial philosophy.

While U.S. Senators are “always trying to get at the results a judge is going to reach, and I pay more attention to their methodology, approach, and understanding of a well-defined judicial role,” Leo told The New Yorker.

Leo already knew a lot about Gorsuch, because the jurist, like Justices Clarence Thomas and Samuel Alito, had participated in programs sponsored by The Federalist Society, which helps conservative-minded law school graduates get more involved in matters of legal policy, and thus challenge the influence of predominantly liberal graduates from elite law schools.

When The Federalist Society was founded in the early 1980s, the late Justice Antonin Scalia was the organization’s first adviser at the University of Chicago, where he served as a professor of law. “We thought we were just planting a wildflower among the weeds of academic liberalism, and it turned out to be an oak,” Scalia observed in hindsight.

Leo explained his mission:

The key was to figure out how to develop what I call a ‘pipeline’—basically, where you recruit students in law school, you get them through law school, they come out of law school, and then you find ways of continuing to involve them in legal policy. So you have these chapters, you have practice groups, you have a pro-bono network, you have a media program—you find ways of engaging these lawyers so that they can still be involved.

Steven Teles, the author of “The Rise of the Conservative Legal Movement,” told The New Yorker:

The most important thing they do is give conservatives a chance to meet one another and check one another out. All that activity lets people bubble up. It creates a chance for people to develop reputations.

Through The Federalist Society’s membership and affiliated groups, Leo is networked with an estimated 70,000 lawyers, and experts describe the group as much more than an organization, more like a “movement.”

Now that Leo is so closely identified with the selection of Justice Gorsuch, he will also be held responsible if the Colorado native does not hew to an originalist philosophy and aligns his opinions with the court’s liberal wing. Likewise, if Gorsuch fulfills Trump’s expectations, Leo will be tapped to lead the selection of the next nominee, when Justice Ruth Ginsburg or Justice Anthony Kennedy retire.