If the USA and Mexico set different thresholds for the poverty line, with the Mexican threshold being lower, then people above the Mexican poverty line but below the USA poverty line could emigrate. This would raise the poverty rate in both countries, but this is an artifact of the two countries differing definitions of poverty. But if you measured poverty in the entire USA+Mexico region using a single definition of poverty, you would see it decrease, assuming those immigrants are better off after moving. (Note that actually measuring poverty this way is difficult due to factors like differing currencies with exchange rates varying over time, so the concept of a unified poverty definition is mostly just theoretical.)

Fun fact: most immigrants from Mexico are not poor-relative-to-Mexico.

Are we talking about immigrants or "immigrants"? I seriously doubt the immigrants of the illegal -- excuse me, "undocumented" -- variety are anything but poor. That's the reason the Mexican government is so eager to keep the whole thing going -- they get to simultaneously foist their poor upon the US while said poor send back billions in remittances. It's a major industry for Mexico, believe it or not.

Net illegal immigration from Mexico has been negative since 2009. http://www.pewresearch.org/fact-tank/2017/03/02/what-we-know...

That's because one person can be deported multiple times and the definition of "Deportation" has changed to include those apprehended at the border.

Can you provide more credible data on this?

Two seconds of Googling would have led you to this:

http://www.latimes.com/nation/la-na-obama-deportations-20140...

Which I'm sure you'll find credible since it's a left-leaning source.

That article does not dispute the claim that net immigration from Mexico has been negative.

Well duh, because it explains how the definition of deportation has changed to include catch and release, which wasn't the case beforehand. This is literally an article reassuring Democrats that Obama's deportation numbers are higher but don't fret about it, because it's not really the case.

Nobody knows for sure. There are only guesses for the number of immigrants and the net migration flow.

It takes a certain minimum amount of education and money to attempt the crossing. Poor yokels who try it get caught or die in the desert.

It also takes a minimum amount of ambition; lazy slobs can't be bothered. Fearful people don't want to risk being robbed or spending weeks out of work to end up deported and gaining nothing.

My relative's wife made the crossing because her husband was abusive and beat her and her son; he threatened to kill them both and had the connections to get away with it.

I'm not surprised. There are one or two particular foreign-crazed states in India where people often spend ~$50k on people to smuggle them across into Western Europe/US. They come apparently as refugees "fleeing religious persecution", but I fear this is often a mere ruse.

The routes they takes are often batshit crazy - the usual Afghanisthan-Egypt/Turkey-Europe route or the Guyana-Mexico-Texas/Cali route (this all the way from India!).