Almost 10% of the potential electorate is foreign born naturalized citizens like me and my parents. Most of these folks aren’t liberal. They are in a political alliance which is based on white liberals supporting immigration and certain welfare systems, and non-white immigrants looking the other way on cultural issues.
I've attempted to find evidence, and found this study, which indicates that first generation immigrants are actually very close to 4th+ in terms of welfare and taxation : https://www.cato.org/publications/economic-development-bulle...
At the same time, I found other studies showing that second generation immigrants support many left wing social policies, such as gay marriage and multiculturalism, but that recent first generation were slightly less inclined to support gay marriage.
It would seem that on the balance, naturalized immigrants (many of which are considered second generation in that study) are on the left socially but not necessarily economically.
What country are you originally from? I’m a first generation immigrant from South Asia, and in my experience, support for socially liberal policies in these communities is often based on compartmentalization. For example, Hindu Americans may support multiculturalism, insofar as they are religious minorities in a Christian majority country. But 70% also support Modi, who definitely doesn’t have a multicultural vision of India: https://theprint.in/india/49-of-indian-americans-back-pm-mod.... One rule for their own country, different rule for someone else’s country. Similarly, most Muslim Americans support gay marriage. But not in their own families: https://www.cnn.com/2019/05/28/us/lgbt-muslims-pride-progres....
That’s why liberals like immigrants. When they seek to change American culture, immigrants like my parents think “well let the Americans do what they want.”
This is in fact why the republic is structured as it is, should we pretend people are inherently good and switch to a simple democracy that can vote for its first genocide next week?
It can be useful to think of immigration as a species of (or perhaps just analogous to) the Monte Carlo method [0].