To partially address this question, I submit the following, snippets of dreams that I've recorded and mostly forgot about, until recently. I did a simple search of my dreams beginning in 1991, and nowhere is there any reference to, or discussion of, Mexican nationals, until 2010. And then, suddenly, this appeared:
I went to the parking lot and saw that there was a fancy red '50s car was parked near my truck. I thought that it was driven by my brother or my father but discovered instead that it was owned by some menacing Mexicans. I left the truck to go back to the building and when I returned a while later I found to my horror that my vehicle (which became a black van) had been stolen by the Mexicans. I raised my keys, however, and floated through the air to where the van had been dumped, which was over some hills in a wooded alcove. The van was turned over on its hood, and people were crawling out of it. I said that I would insist that the vehicle be totaled so that I could get full value for it. (November 14, 2010)
I dreamed that I was returning from a visit to some place. I visited a sort of enclave that was filled with Mexicans. It looked a bit shabby, filled with booths selling goods. I was also looking for my blue camping cooler, which I was obsessed with locating. It had the blue ice bricks in it. I asked one of the Mexicans about it, and he showed me a blue cooler, but I recognized it as not being mine. I was staying at a family's house. The whole dream had a strange feel to it. (December 16, 2010)
And then, in 2015:
This morning I had a series of dreams about moving into a house. Some men from that area came to the kitchen door of the house, which opened to the street. One of them was soliciting for a contribution. He said the he and several with him were trying to raise money to travel back to Mexico. I said that I would give him money if he promised to share it with his friends, and he agreed. I gave him five dollars and he promptly said that he would keep it for himself. I chided him for this, but I got the impression that these weren't bad people. I saw a menacing person approach and I got my Magnum and put it nearby. A bit later, I was talking with one of the men and they admitted that they were "dead." I thought that having a pistol, then, was unnecessary.
At the time that I transcribed the dreams, I thought little of them (I do tend to have strange dreams), but now I wonder: Where did they come from? I do not consciously harbor any prejudice against Mexican citizens. My personal experience with Mexico has always been positive. But the stereotype of the "menacing" or shabby Mexican surfaced in my dreams long before it became a political issue. Is this a subliminal image that I somehow picked up from the universally negative coverage of Mexico by the American media? If so--who has a vested interest in its creation, and exploitation?