You mean that they vote like the Americans who are not Christians, if they voted with the majority of the Christian Americans who are not Catholic, then things would be very different.
The Catholic vote has helped collapse the culture by being a force for the left, and not just in feeding the corrupt big city machines and unionism, for instance the non catholic Christian vote went against FDR in 1940 and 1944, just as it went against Truman and Kennedy, and Clinton and Al gore, Obama and so on.
America is coming to resemble it's Catholic neighbors, in corruption and moral decay, and the vote determines that path.
Or maybe it's t'other way around.
Maybe some religious sociologist will have to look at this more comprehensively than either you or I have done so far, but I have seen the exact symmetrical opposite of what you say. Seriously.
What I have seen --- since at least the age of nine, when I started noticing things, and that would be 1960 or so --- is a recurring current, inside and outside the Catholic church, pushing Catholics to be "more American."
As early as 1898 Pope Leo XIII detected this tendency in its larval form and coined a new term, "Americanist heresy," to describe the overall bias in favor of Catholic assimilation to WASP political and ecclesial ideals. I, personally, don't recall any public figure from my childhood ever saying he seriously wanted to make America more Catholic (I will salute the single saintly exception of Bishop Fulton Sheen) but I couldn't count on all my fingers and toes the number of times we were nudge, nudge, nudged to be more miscible, more Vacation-Bible-School, more Boy Scout, more American.
Jack Kennedy, after all, appealed to the electorate, not by saying he was such a comprehensive Catholic, but by pledging in public that he was nothing of the kind. He swore he had no truck with creeds or popes, policies or preferences, traceable to the Catholic Church. His famous address to the Greater Houston Ministerial Association was just the capstone of this series.
Prominent Catholics were constantly trying to shuck their "distinctives" --- whether minor or major, whether it was changing their non-WASP surnames (how many thousands of Schmidts became Smiths?) or effacing their own monuments (the Church "Wreckovation" movement which stripped down Catholic sanctuaries until they looked like they'd been vandalized by Calvinist iconoclasts).
Our Catholic youth groups either went toward Pentecostalism (Charismatic) or Youth Band Praise Chorus. Teenagers of my generation were given the idea they could reinvent liturgies along the lines of any Jesusy Godspell impulse. Our hymnals were filled with Protestant ditties--- not all bad, mind you, I can love me some Wesley or Watts --- but just thin, thin and banal when compared to the treasuries of Catholic liturgical music which were thrown by the boxful into the dumpsters around 1965-75.
Three generations of people-pleasing priests became assertively "ecumenical" --- happy to encourage the view that "We're Just Like You" -- "You" being anything that isn't papist.
And anyone who pushed for something that would disturb the neighbors as being intellectually, culturally or politically Catholic, was chided for being Triumphalists or tribalists or paleo-something.
"Parochialism" was a bad word, and Federal and local governments cooperated to break up or bulldoze parish-based ethnic neighborhoods --- and of course that means Catholic voting blocs--- often under the pretext of "urban renewal" (we called it "urban removal.") E. Michael Jones was right about that (LINK)
In things large scale and small, the prevailing wind was always pushing Catholic Americans away from "Catholic" and toward "American," which could have either a secularist or a Protestant tinge (in my childhood America was still culturally Protestant) but it was always "NOT the way you did things in Rheinpfalz" (or Galway or Gdansk).
So politically, we've got Catholic Supreme Court justices indistinguishable from Episcopalians, and Catholic Congressmen that palaver like Methodists? And Catholic voters that vote (within 1 percentage point plus or minus), like Everybody Else? Imagine my surprise.
The whole problem with the Catholic voters; the Catholic politicos; the Catholic opinion-leaders; is that they are not Catholic enough. I would be a happier woman if they were all members of the Catholic faction of the Catholic Church. And you might be more satisfied --- or if not, you would have a quite different set of things to complain about.
It could be objected that I am painting with a broad brush --- the polemic form has something to do with that --- but manifestly, in my lifetime, American Catholics became more assimilated to American Broad Church Christianity; not the reverse; and I'd say for worse.