How did we get here?
Wikipedia gives one quick rundown.
Other Catholic justices included Pierce Butler (appointed 1923) and Frank Murphy (appointed 1940). Some accounts note that Sherman Minton, appointed in 1949, was also a Catholic; however, during his time on the Court he was a Protestant, though his wife’s Catholic faith was noted at the time in relation to the notion of a “Catholic seat”.[71] Minton joined his wife’s Catholic faith in 1961, five years after he retired from the Court.[72] Minton was succeeded by a Catholic, however, when President Eisenhower appointed William J. Brennan to that seat. In fact, Eisenhower intently sought to appoint a Catholic to the Court—in part because there had been no Catholic Justice since Murphy’s death in 1949, and in part because Eisenhower was directly lobbied by Cardinal Francis Spellman of the Archdiocese of New York to make such an appointment.[73] Brennan was then the lone Catholic Justice until the appointment of Antonin Scalia in 1986, and Anthony Kennedy in 1988.
Like Sherman Minton, Clarence Thomas was not a Catholic at the time he was appointed to the Court. Thomas was raised Catholic and briefly attended Conception Seminary College, a Roman Catholicseminary,[74] but had joined the Protestant denomination of his wife after their marriage. At some point in the late 1990s, Thomas returned to Catholicism. In 2005, John Roberts became the third Catholic Chief Justice and the fourth Catholic on the Court. Shortly thereafter, Samuel Alito became the fifth on the Court, and the eleventh in the history of the Court. Alito’s appointment gave the Court a Catholic majority for the first time in its history.
And the Vatican’s triumph was complete.