As blogger Steve Sailer notes, a Pew Hispanic Center survey in 2005, near the peak of the housing bubble, reported that 22 million Mexicans would immigrate to the United States as legal guest workers if that was possible. The Pew and Gallup numbers are not commensurate, since Pew asked a hypothetical question and Gallup asked about general desire to immigrate, but there’s a huge difference between 22 million and 5 million. In the debate on immigration policy Sailer and Mickey Kaus have argued that large-scale illegal immigration from Mexico will likely resume when the U.S. economy revives and if a comprehensive immigration law provides legal status for many or most current illegal immigrants. I have predicted that we will never see the kind of large-scale Mexican immigration to the United States that we saw in 1982-2007. I think the Gallup numbers tend to support my prediction. Desire to immigrate does not usually yield a decision to immigrate. People take the plunge of immigration not just to make money but to pursue dreams or escape nightmares. For Mexicans these days the United States is less of a dream and Mexico is less of a nightmare than in the years from 1982 to 2007. 

It's called convergence: Mexico becomes more like America (good in theory, although the obesity data raises a disturbing counter-example), while America becomes more like Mexico.

But, here's a suggestion. The construction industry is just starting to pick up again, and contractors are starting to make houses-rotting-in-the-fields noises about how there are "shortages" of construction workers and they need to get their workers back from Mexico. So, why don't we wait five years and see what happens with immigration before passing some massive immigration "reform" law based on suppositions about how It Can't Happen Again?

Test case: Puerto Rico. The huge influx of Puerto Ricans to New York City that started in the late 1940s abruptly ended in 1961, when incomes in Puerto Rico reached one-third the U.S. mainland income level. There were and are no legal barriers for Puerto Ricans, who are U.S. citizens under an act of Congress passed in 1917. They just stopped coming. Recent years have seen some movement of Puerto Ricans to the Mainland (probably more to metro Orlando than metro New York), but it’s nothing like the magnitude of the 1949-61 migration. The data suggested that Mexicans just stopped coming to the United States in 2007, when the housing bubble burst and the recession began. I’m betting—aware of the nontrivial possibility that I could be wrong—that we won’t see another massive wave of immigration from Mexico.

Perhaps, although the tax breaks given to American corporations to prop up the economy of Puerto Rico, to stop the Puerto Ricans from coming, are lavish. Bribing Puerto Ricans to not be nationalists is enormously expensive on a per capita basis.

Moreover the Puerto Rican population in the U.S. is growing steadily, despite mostly living in low birthrate East Coast cities. According to a new study, the Census Bureau found 2.7 million Puerto Ricans in 1990, 3.7 million in 2000, and 4.6 million in 2010. Over the same period, the population of Puerto Rico itself grew slightly from 3.5 to 3.7 million (but the population of Puerto Rico is down compared to 2000.)

So, that's 74% growth over two decades.

Puerto Ricans, both in P.R. and in America, have low fertility, although the population can keep growing due to "demographic momentum"? (E.g., somebody with four children can have eight grandchildren a lot more easily than somebody with two children can have eight grandchildren.)

But, it's also true that Puerto Rican immigration has been substantial for the last seven years, despite the recession here.

Here's a good 2012 article by John Marino on Puerto Ricans immigrating to the U.S.:

Puerto Rico residents continued their exodus from the island over the past year during tough economic times, with the local population shrinking by 19,099 residents, or 0.51 percent, the biggest percentage loss by far of any U.S. jurisdiction, according to the U.S. Census Bureau. 

The population loss was due to migration to the U.S., with a net 35,469 residents lost to out-migration [that a net of almost 1% of the population leaving in 1 year], while island births outpaced deaths by 16,370 during the 15-month period covered by the new Census data, which runs April 1, 2010 to July 1, 2011. 

The drop-more than double the average annual population loss reflected in the 2010 Census for the previous decade- is part of the first new U.S. population estimate released by the bureau since the 2010 Census, which showed the island's population had declined by 82,821 people, or 2.2 percent, over the past decade. ...

Back in October, an Ipsos poll commissioned by WAPA-TV found 45 percent of islanders have considered leaving Puerto Rico in search of a better quality of life, with the majority of those setting their sights on the States. One-quarter (25 percent) of those who have considered a move from the island have taken concrete steps to do so, the poll found. 

Projected over the entire population, the poll results indicate some 1.5 million people would consider leaving the island, while 419,000 of those have at least started a plan to move. ...

Puerto Rico's population was pegged at 3,725,789 in the 2010 Census, down from the 3,808,610 registered in the 2000 Census. It marked the first time the local population had declined between census counts. 

The 2010 Census also showed there were 4.7 million Puerto Ricans living in the States, which was the first time more Puerto Ricans lived stateside than on the island. 

Puerto Rico is richer than Mexico in terms of per capita GDP, although Puerto Rico has been declining and Mexico improving.

In contrast, the Census found the number of individuals in the U.S. self-identifying as of Mexico origin growing from 13.4 to 31.8 million from 1990 to 2010, a growth of 137% or a little less than twice as fast as the growth in the Puerto Rican population.

It's crucial to note that a huge number of births to Mexican women in the U.S. are within a decade or so of arriving in this country. That's why the Mexican Total Fertility Rate has dropped sharply since the Sand State housing bubble popped — fewer immigrants means fewer women arriving to have the 3 or 4 kids they can't afford to have in their own country. The last amnesty caused a big baby boom among the amnestied, and there is no reason to imagine the next one wouldn't do the same.