It is common knowledge that the under-protected border to the south is a big security risk for terrorism as well as the economic instability caused by "undocumented workers", I prefer to call them illegal. THey are breaking the law, that is that. There is a legal way for them to enter and they need to make use of that if they want it so bad. I personally prefer the original Immigration Act of 1790 that was created by our forefathers. That act limited immigration to people who were worth a salt. It said that you had to be a white wealthy landowner. Landowners were looked upon to be people who would contribute to society since they sought their own self-improvement. This law was altered very little until 1965 when it was basically scrapped and replaced by a new policy that basically allows anyone in. It used to be that you had to be a worthwhile contributor to society and now they will take any deadbeat from any country.
Finally, the last thing I have to say about immigration from third-world nations, is that those nations are a third-world for a reason. The success or failure of a nation is dependent upon its people and not geography, climate, etc. If that were true, Haiti would be rich and Iceland would be poor. If a people can't make their nation functional in their homeland, they certainly won't make this nation functional either. We will descend to their level of "third-worldism" as our first-world population is replaced by them. Also, people who don't understand the concepts of freedom that were created by our Constitution won't uphold it. Some of the restrictions that are in place today would have had been the cause of a civil uprising 200 years ago. If Andrew Jackson told people they would have to register their firearms, every man with a spine would have been marching towards his Presidency.