Demographics didn’t create a 150 year history for the Catholic vote, and demographics don’t mean much in a church that is a single church, a single denomination, under a single authority, and under a single teaching.
Yes, immigrant Catholics found a political home in the demagogic Democratic party which did not challenge them to rethink their notion of government.
But since VATII in this country (and probably in Europe as well) a bunch of bishops, priests, and teachers just ignored those parts of the social teaching which they didn't like. I remember assisting at a class in which the deacon taught as a wonderful doctrine something explicitly rejected in Veritatis Splendor by JPII.
As a convert I came, so to speak, "cold" to the social encyclicals and found that they did NOT AT ALL favor the top-down government and delegated charity espoused by socialists (and too many Catholics.)
I'm seeing a shift. Mind you. I've only encountered a VERY small sample. But among the Dominican friars, those older than around 50-55 TEND to be pinkos. Those younger than 50 tend to be conservative.
Among the university students whom I encounter in parish work, including many "converts", there are a several who are members of the campus "Burke Club."
And I can say this. Those I see at Mass regularly -- on Sundays and weekdays, are far more conservative than the Easter and Xmas Catholics or the "converts" who give every impression of coming to our classes or Masses to get their ticket punched. That is, the Burke Club Catholics come to Mass. The pinko Catholics, not so much.
To restate that, the Catholics who are loyal to the Magisterium and committed to Catholic piety tend to be conservative politically. On the other hand, the socialista Catholics are so far from the teaching to the Church that they are frequently incoherent. It's not just that they don't know what "proximate material cooperation" in a sin is, they don't WANT to know and resent the very activity of careful analysis of ethical or theological issues.