GWB got over 40% of the Hispanic vote in 2004. Mexicans tend to be very conservative. That's the truth in California as much as it is in the South. These conservative roots match the Republicans more so than the Democrats, but it's the immigration stance that has tilted Hispanics towards the Democrats, but only recently, and even that is probably a temporary thing.
The notion that the Democrats have Hispanic (and especially Mexican) voters locked up isn't a reality.
> The only big issues are political externalities - i.e., Mexicans might vote for politicians that make the US more like Mexico. That's an issue even in the US (California refugees voting for CA-like policies in their new states), and is best solved with disenfranchisement/reduced democracy rather than trade barriers.
To be clear, regardless of your political stance or your views on immigration, not giving illegal immigrants the right to vote is not the same as disenfranchisement or reduced democracy. For legal migrants, am not aware of anything showing actual attempts at disenfranchisement.