GOP presidential candidates are falling over themselves to get on record with tough immigration plans. A string of them — Rand Paul, Chris Christie, Lindsey Graham, Scott Walker, Bobby Jindal and Rick Santorum — have spoken out in some form against birthright citizenship. That's the idea that being born on U.S. soil, regardless of your parents' legal status, automatically makes you a U.S. citizen.
Ben Carson went even further, saying he wants to secure the border — where he claims there are caves in which immigrants can hide — by using drones.
"You look at some of these caves and things out there, one drone strike, boom, and they're gone," Carson said.
When it comes to the issue of birthright citizenship, while some conservatives disagree, a lot of legal scholars believe it is settled law, enshrined in the 14th Amendment of the U.S. Constitution, and that it therefore would be fantastically difficult to overturn.
The flurry of tough positions on birthright citizenship is yet another sign of the power front-runner Donald Trump, with his bombastic anti-immigration rhetoric, has in the 2016 GOP race. The question for other Republicans is how to take tough — but still palatable for a general election — stances on the issue.
Both Florida Sen. Marco Rubio and former Florida Gov. Jeb Bush have defended birthright citizenship, but they have said more needs to be done about women who might come into the U.S. expressly to have children. It's unclear exactly what they would — or could — actually do.
"If there's abuse, if people are bringing, pregnant women are coming in to have babies simply because they can do it, then there ought to be greater enforcement," Bush told conservative radio host Bill Bennett this week, as reported by Politico. "That's [the] legitimate side of this. Better enforcement so that you don't have these, you know, 'anchor babies,' as they're described, coming into the country."
When pressed on his use of the phrase "anchor babies," Bush defended it. "If there's another term that I come up with, I'm happy to hear it," he said Thursday. (Hillary Clinton jumped at the opportunity, tweeting, "They're called babies.")
Rubio told voters in Iowa this week, as reported by the Wall Street Journal, "I'm open to doing things that prevent people who deliberately come to the U.S. for purposes of taking advantage of the 14th Amendment, but I'm not in favor of repealing it."
The problem is that it's not certain exactly what the government could do to stop this from happening. (Neither the Bush nor the Rubio campaign has responded to requests for comment from NPR.)
What the U.S. could do to prevent (the few) "birth tourists"
The closest thing to a law that could slow foreign women from having babies in the U.S. is that you can't lie about why you want a visa to the U.S., said Muzaffar Chishti, director of the nonpartisan Migration Policy Institute's office at New York University.
"If you're a Chinese woman coming to the U.S. as a tourist, you are making a representation to the U.S. government that I am coming to be a tourist," Chishti said. "If it is established by a consular officer that the woman is not really coming for tourism, but is coming to deliver a baby, you can deny the visa. There's no doubt about that."
But that's tough to enforce under current regulations, says Mark Krikorian, executive director of the Center for Immigration Studies, a think tank that tends to advocate tighter immigration policies.
"It's not illegal [for a foreign tourist to have a baby in the U.S.], though the State Department could put through regulation if they wanted to try to stop it," he says, for example, by more pointedly asking pregnant women if they're coming simply to have a baby in the U.S.
This phenomenon of having a child on a tourist visa has come to be known as "birth tourism," and many of the stories about it in the past few years have tended to center around women coming from China, where families are restricted in the number of children they can have.
In addition to asking more questions of pregnant women entering the country on tourist visas, likewise, Chishti said the government could crack down more on the clinics — or "maternity hotels," as they are called — where these women routinely go to give birth.
Of course, that only applies to unauthorized immigrants who go through the visa process. The number of "birth tourists" may indeed be very small. Earlier this year, the Center on Immigration Studies, which favors more tightly monitoring "birth tourism," estimated that there are 36,000 such women annually.
Stopping other immigrants from having children is a different story
But there are millions of undocumented immigrants who entered the country illegally. Because the law didn't detect many of them when they came in, trying to stop them from having children is difficult, to say the least.
Likewise, millions of unauthorized Americans came in legally but have overstayed their visas. Improving the entry-exit monitoring system could do a lot to bring down the unauthorized immigrant population, Chishti said. But that doesn't mean anything about their children.
"To be sure, this recommendation applies to reducing the pool of unauthorized in general," he said, but "does not specifically address the 'anchor babies' phenomenon, because most likely mothers would deliver babies during their periods of authorized stay."
It's also possible that trying to crack down on the birthright phenomenon simply means tightening existing laws and enforcement. Krikorian says that would have been a smarter answer to the birthright question for Bush and Rubio.
"A better-thought-out, more humane response would have been, when we enforce immigration laws better, in general, there will be fewer people here to give birth who are not citizens or green card holders," he says. But as it stands, he adds, simply calling for better enforcement against these so-called "anchor babies" is, to him, a non-answer.
"It's their way of seeming responsive without supporting a change in our citizenship practices," he says.
So, how many children are born to illegal immigrants every year?
There are no exact counts on the number of U.S. children with unauthorized parents, but some organizations have tried to count.
The Pew Research Center found in a 2012 report that around 5.5 percent of all K-12 students were U.S.-born citizens who also had at least one parent who was not authorized to be in the U.S. Still, many of those children may have one parent who is here legally.
The center also estimated in 2008 that 340,000 of the 4.3 million children born in the U.S. — not quite 8 percent — were born to immigrants who were in the U.S. illegally.
Those are rough estimates, but they suggest that while the so-called "anchor baby" population is relatively small, the practice of immigrants who are in the U.S. illegally having babies in the U.S. is a very real phenomenon.
And that puts candidates in the tough spot not only of deciding whether they think that's a problem, but also if and how they could fix it.