They are Hispanics, not Mexicans, and they have nothing to do with the many generations of liberal Catholic voting, Hispanics only showed up recently.
Catholicism is liberal and creates liberal democrat voters, the thread topic describes part of that historical effort to break America from it's roots and Europeanize it.
“Hispanics” includes a lot of different ethnic groups. The great majority are Mexcians. The longest in residents are those who families were here in 1848. But they are a small minority, as upper California was not settled until the 1770s. New Mexicans can be traced to the 1590s, Tejanos in the Rio Grande Valley of Texas have been there since the early 1700s. Until recently, most Mexicans in the United States came from the Mexican states bordering the northern border. In Texas the real ethnic border was the Nueces River. That is until the railroad penetrated to the Valley, and midwestern famers came in and plundered the lands that had belonged to rancheros forever. In the 1920, San Benito in the Valley was a major KKK center, since the biggest Klan center was Indiana.