It should also be noted that this coincides with a lot of the states implementing much tougher penalties on employers that knowingly hire illegals. Many states require that employers use the E-Verify system before hires, and if an illegal can't get a job, then it stands to reason that all they can do is go home. In an economy like this, illegals work for peanuts compared to legal residents, so if anything, you'd think less-than-scrupulous employers would actually employ more illegals, not less. But that's just my logic on it, which may or may not be the case, seeing as how I don't own a business and wouldn't employ illegals, regardless.
It will be interesting to see how their economy deals with the re-influx of their people earning money here. Much of the capital earned by illegals was sent directly back to Mexico, which greatly helps their economy. Also, they've not had to support them through their social infrastructure, instead basically exporting their poverty to the US (most illegals, unfortunately, are not high-skill workers or highly educated), so I suspect that may be a drag on their economy as well. That being said, they do a lot of manufacturing, so it may help them in the long run.
I have to admit, I am tired of the "declining America" bit, not because it's not currently true, but because most of us act like there's nothing that can be done about it.
(Also, pegging the majority of USA residents as descendants of illegal migrants is a bit of a stretch.)