Despite the rhetoric, the "border crisis" in the Rio Grande Valley is a relatively minor one, in terms of numbers.

The thousands of families and children traveling alone from Central America who have crossed the border into Texas in recent weeks present an emergency for federal immigration agents, who are ill prepared to care for so many children and are not allowed to send them back to their countries of origin. In the past year, the Border Patrol has apprehended nearly 40,000 unaccompanied minors in the Rio Grande Valley, up from 14,000 the year before.

The Rio Grande has been the site of most of the border crossings because the migrants, for the most part, are not from Mexico. Instead, they're from the "northern triangle" Central American countries of Guatemala, Honduras and El Salvador, meaning that the most direct route to the U.S. from their hometowns is through the tip of South Texas.

While Customs and Border Protection agents can immediately return underaged Mexicans or Canadians who enter the country illegally, federal law requires them to take children from non-contiguous countries into custody and place them with the Department of Health and Human Services for care.

Including families, CBP has stopped about 180,000 “other than Mexicans” over the past 12 months, 140,000 of them in the Rio Grande area.

That has created severe problems for the federal officers trying to kept the families and children housed and fed while determining their fate.

But because Mexicans are not illegally crossing the border en masse, the overall impact of the influx so far is mostly limited to Texas and is relatively small.

Although it is difficult to quantify illegal immigration, because it takes place off the grid, available data suggest that total illegal immigration to the U.S. is down.

According to Pew Research, which publishes estimates of the number of people living in the U.S. illegally, that population peaked at 12.2 million in 2007. The immigrants were mostly Mexicans, disproportionately working-age men, crossing the border to the U.S. But then the recession hit, and the lack of jobs caused illegal immigration to stall. The number of illegal immigrants in the U.S. bottomed out at 11.3 million before ticking up in 2012, the most recent year for which data is available, to 11.7 million.

The decline in the population of unauthorized immigrants was also led by Mexicans. That country's speedier economic recovery and declining fertility rates are “reducing the push factors that have been bringing Mexicans to the U.S.” according to Pew Research’s Michelle Mittelstadt.

Experts don’t see a resurgence in Mexican-U.S. migration “to a large extent,” said Mittelstadt, because “Mexico is now able to generate better economic opportunities and jobs for its citizens.”

And while immigration from the poorer and more dangerous Central American countries has picked up, the influx is not enough to offset the slowing of immigration from Mexico.

The illegal alien apprehensions reported by the Border Patrol also show a drop in border crossings. The 180,000 “other than Mexicans” stopped by the Border Patrol in the past year pales in comparison to the 1.6 million apprehensions of immigrants, mostly Mexican, in 2000.

That year, 240,000 illegal immigrants were stopped by the Border Patrol in Southern California alone.

Even just in the Rio Grande Valley, this year’s surge is not likely to rival the rush of the late 1990s, when the Border Patrol stopped more than 200,000 border-crossers three years in a row.