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Today, Catholics lead every branch of the US government. Has Catholic representation at the highest levels of American government ever existed to this large of a degree before and when/how did Catholicism become acceptable to the American Protestant mainstream? written by u/USReligionScholar

It’s difficult to find a proper point in time to begin properly answering this question, but let’s start with the First Vatican Council, also known as “Vatican I”, which took place in Rome in 1869-1870.

Pope Pius IX convoked the council to develop a comprehensive Catholic response to what he called “contemporary problems.” These “problems” included rationalism, liberalism, materialism, and allegedly related secular political philosophies such as anarchism and Communism. This was a continuation of the Church’s efforts to combat these philosophies in the latter half of the 19th century, for example through Pius IX’s 1864 encyclical The Syllabus of Errors, which listed what the Pope saw as grave misunderstandings (to put it mildly) of the Church’s role in the world and attempted to correct the record by citing relevant doctrine.

Most notably, Vatican I, after hot debate, declared the dogma of papal infallibility – reaffirming the strict hierarchy of the Church, in a rebuke of Catholic progressives and reformers who had advocated for the Church to adapt some of its stances for the modern age.

What does this have to do with American judges? Let’s jump ahead a bit to the encyclical Testem Benevolentiae Nostrae (1899), in which Pius IX’s successor, Pope Leo XIII, wrote to the Archbishop of Baltimore expressing concern about the dangers of a body of thought that he called “Americanism.”

This encyclical draws a direct connection between the animating concerns of Vatican I and the then-emerging superpower of the United States of America, a country explicitly founded on Enlightenment ideals that the Church feared were inherently contradictory to Catholic precepts: individual self-determination, near-absolute freedom of expression, acceptance of all faiths as inherently valid, the supremacy of a secular government… the list goes on. Even if America the nation never fully lived up to these ideals, they were still valorized by American political culture and by Americans themselves writ large.

Paradoxically, the roots of over-representation of Catholics in the American judiciary (including the Supreme Court) compared to their share of the general population can then in part be traced to the separate institutions that Catholics established for themselves in the United States that were intended as bastions of Catholic tradition and thought in a sea of secularism.

While Catholics established a variety of organizations for this purpose, including social clubs and charities, most relevant to this discussion were Catholic schools and universities. These guaranteed not only the inculcation of Catholicism among generations of Americans who may have otherwise drifted away from the Church, but the propagation of legalistic Church responses to encroaching modernity. This became all the more pronounced as prominent Catholic universities added schools of law, e.g. Notre Dame (1869) and Georgetown (1870).

Students at these law schools would likely have studied encyclicals such as Pope Leo XIII’s Aeterni Patris (1879), which laid the foundation for what would become the jurisprudence of “natural law,” in contrast to the more fallible laws of man.

So, let’s sum up a complex history by stipulating that a critical mass (heh) of Catholics in America had the right institutions, knowledge, and motivation to attempt to preserve what they saw as timeless fundamental values through judicial means.

However, anti-Catholic sentiment precluded much action on this front until the post-WWII era. At this time, Catholics were becoming more and more accepted in mainstream American politics, for reasons detailed in the post by /u/USReligionScholar linked elsewhere in this thread. Despite the fact that American Catholics as a whole were not strictly associated with either major party – if anything, working-class Catholics had been solid Democratic voters for quite some time – elite conservative Catholics had an opening to reshape the American conservative movement and American politics as a whole.

One such was example was Yale graduate William F. Buckley, Jr., prolific author and founder of the magazine National Review. Despite the dominance of Protestants in American politics in general and conservative politics in particular up to this point, Buckley was able to establish National Review as the leading organ of postwar conservative thought, featuring many Catholic writers in addition to himself.

Buckley and his cohorts articulated a philosophical and legalistic underpinning for what would emerge as guiding principles of the conservative movement during the Cold War, such as anti-Communism and anti-secularism. This movement became more organized and forceful in the aftermath of Supreme Court decisions like Griswold v. Connecticut and, especially, Roe v. Wade – those that protected (or, depending on your perspective, invented out of whole cloth) a personal right to privacy, particularly sexual and reproductive autonomy.

For adherents of “natural law,” this was unconscionable, so the federal judiciary and especially the Supreme Court became targets of a concerted effort to reverse what those like Buckley saw as decades (if not longer) of decadent and wrongheaded liberal jurisprudence.

One of Buckley’s enduring achievements, along with fellow conservative thinkers like Leo Strauss, was to bridge the gap between muscular American patriotism and Catholic dogma, which to that point was quite opposed to the ideals behind the American experiment. Ironically, as the Church itself liberalized in the 1960s, notably through the Vatican II conference, American conservatives were more easily able to bring their Catholic identity in line with their version of American values.

Meanwhile, though conservative Protestants were surely integral parts of the postwar right-wing movement, the advent of a new generation of legal scholars, writers, and organizers, not to mention judges themselves, was distinctly (though of course not entirely) Catholic. To put it briefly, this was because there was simply no equivalent history of Protestant jurisprudence and related institutions to draw on.

(Richard Hofstadter noted the distinct antipathy of evangelicals in particular to rigorous theology in his seminal Anti-Intellectualism in American Life (1962); writing in The Atlantic in 2000, Alan Wolfe said that “evangelical Protestantism, at least in its twentieth-century conservative forms, ranks dead last in intellectual stature.” Wolfe also noted that while three Catholic schools were ranked in the top 50 of research universities, there were no explicitly evangelical schools in that echelon.)

So whether out of necessity or principle or some combination thereof, conservative Protestants overcame whatever antipathy they may have felt toward Catholics in order to benefit from their Papist brethren’s legal acumen. As evangelical historian and author Mark Noll wrote in 2004: “So rapidly has the situation changed from the cold war that existed into the 1960s, that it is now barely conceivable that either Catholics or evangelicals could once have thought that either could get along without help from the other.”

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I think part of the OP's question went unaddressed.

In 2002, the U.S. Supreme Court justices were (in order of seniority):

William H. Rehnquist (Protestant, appointed by Republican)

John Paul Stevens (Protestant, appointed by Republican)

Sandra Day O'Connor (Protestant, appointed by Republican)

Antonin Scalia (Catholic, appointed by Republican)

Anthony M. Kennedy (Catholic, appointed by Republican)

David H. Souter (Protestant, appointed by Republican)

Clarence Thomas (Catholic, appointed by Republican)

Ruth Bader Ginsburg (Jewish, appointed by Democrat)

Stephen G. Breyer (Jewish, appointed by Democrat)

​

So what we see here is that the process explained by u/AffordableGrousing whereby Republicans tended to favor particular types of Catholics hadn't come into effect, really not until George W. Bush got to pick justices in 2005 (which is too recent to discuss here). Republicans had previously appointed Protestants. We also see that the justices can't easily be sorted by which party appointed them: Stevens and Souter, in particular, were considered quite liberal even though they had been appointed by Republicans, with Kennedy and O'Connor also not considered reliable conservative votes.

Interestingly, Reagan's failed 1987 pick and the reputed most conservative nominee ever, Robert H. Bork, was not a churchgoer at the time of his hearings. At the time, he was described in the press as an agnostic, a word to which he objected in his confirmation hearings though without offering a replacement. In 2003 Bork converted to Catholicism, at which time he said that he had actually been an atheist in 1987.

It's also notable that Souter, who took his seat in 1990, was the last Protestant to be confirmed. Currently every member of the Court is Catholic or Jewish. Two Protestants have been nominated, one of whom withdrew (Harriet Miers) and the other is still going through the process (Ketanji Brown Jackson).