The difference between anti-Judaism (the "Talmudic Jewish religion") and anti-Semitism (Jewish people as a race) was first laid out explicitly at a magisterial level by Card Merry del Val when he was Prefect of the Holy Office. The latter was roundly and soundly condemned.
The modern anti-Christian movement, which centres around Liberalism, owes much of its rapid progress to the secret society of the free masons... Freemasonry today is the enemy of the Church and every Catholic Government and Catholic institution in the world. It is closely associated with Modern Judaism (including Rationalistic Jews, as well as those of the Talmud and Cabala); and is largely under Jewish influence and guidance[.]He also founded An Ríoghacht, which would go on to form the basis of Fr Denis Fahey's Maria Duce. Fahey was an anti-Semitic theologian who made frequent references to The Protocols of the Elders of Zion. He was also
influenced by Nesta Webster, an English writer who promoted theories of Jewish involvement in secret societies advocating for revolution. Webster promoted the Protocols, was involved in British fascist groups in the 1930s and influenced the later John Birch Society and many other anti-communist and antisemitic groups. Even Hillaire Beloc described her writing as ‘lunatic’, but Fahey enthusiastically promoted her work to this students.
And Fahey's great disciple in America was of course the notorious radio priest Fr Charles Coughlin, who repeated and indeed republished Fahey's conspiracy theories about how "the Jews" had been behind the Russian Revolution.
Fahey (not to be confused with Fr John Fahy) and Éamon de Valera meanwhile weren't just at the same school (Rockwell College, Cashel*), they were even in the same rugby team. The school itself was a foundation of the Holy Ghost Fathers, of which order Abp Lefebvre would later become the superior.
Lefebvre's great mentor though was Fr Henri Le Floch, the Rector of the French Seminary in Rome who was removed by Pius XI in 1927 for his endorsement of Maurras and Action Française. Le Floch's close friend and ideological ally Cardinal Billot actually "resigned" from the College of Cardinals in protest. Le Floch had of course also had an influence on Fahey, who was himself a distant supporter of Maurras and would later go to become a Holocaust denier.
Cahill died in 1941, after which Fahey effectively took over his political movement. Now calling itself Maria Duce, in practice it did little more than picket cinemas on the grounds that the Hollywood films they were showing were too "Jewish" - the word no longer meaning religion or even race so much as anything Fahey and his mob disapproved of, including (non-Jewish) American actors such as Orson Welles and Gregory Peck. There was also an attempt by members of Maria Duce to infiltrate the Legion of Mary.
By the early 1950s Archbp. John McQuaid, the Archbishop of Dublin, had had enough, and took steps effectively to suppress Fahey's group. After Fahey's death in 1954 it changed its name to Firinne (Truth), after which it survived up until the 1960s.
*I happen to know there was a copy of Cahill's 1932 book The Framework of the Christian State in the school library because said volume is now on my bookcase.
