South Carolina Sen. Lindsey O. Graham (R) says America faces a new and growing foreign threat: illegal immigrants and tourists who come to here for the express purpose of giving birth so their children obtain citizenship.

Sen. John McCain (R-Ariz.) and other top Republicans quickly jumped on the issue and called for hearings.

The senators said their concerns arose from recent reports of a burgeoning "birth tourism" industry, which helps expectant mothers abroad travel to the United States to deliver their babies. They also said that birthright citizenship, which is granted by the 14th Amendment of the Constitution, could provide an incentive for people to enter the country illegally.

The sudden support cheered anti-immigration hard-liners who have been pushing to do away with birthright citizenship for years, but the senators face a problem: Few others want to take up the issue, and it is almost assuredly going nowhere.

Even some of the most vocal critics of the country's permissive immigration laws are skeptical of the efforts, which they say are particularly emotionally charged because they affect children and families.

"We don't think that it is worth the political capital to initiate a debate on this issue," said Jon Feere, legal policy analyst for the Center for Immigration Studies, a think tank that backs stricter immigration policies. "The energy spent on ending birthright citizenship might be better spent reducing illegal immigration through a commitment to immigration law enforcement generally. If illegal immigration is ended, the problem of birthright citizenship for children of illegal aliens disappears."

Nevertheless, raising the issue could prove beneficial to Graham and McCain, both of whom have rocky relationships with many of the conservatives whose support they'll need to stay in office.

Graham has fallen out of favor with many in his party for working with Democrats on a host of issues, including immigration. He was just one of five Republicans to vote last week to confirm Elena Kagan for the Supreme Court, a decision that further raises the possibility that he will face a serious primary challenge when his term runs out in four years.

McCain's concern is more immediate -- he faces voters in a primary later this month and is on the ballot again in November.

"My organization would say there should be a change on the horizon, but not in the way Lindsey Graham is talking about it," said Rosemary Jenks, director of governmental relations for the nonprofit NumbersUSA, the leading group opposed to birthright citizenship. "I do think it is political. . . . What we need is a serious discussion of the actual issues, not a lot of political ploys. "

Bills related to birthright citizenship have been introduced in Congress every year since the 1990s, experts say. They almost never gain traction and rarely attract high-profile supporters such as Graham and McCain. When the issued was raised this year, Senate Minority Leader Mitch McConnell (R-Ky.) as well as Sens. Jon Kyl (R-Ariz.) and Jeff Sessions (R-Ala.) said they, too, would be open to hearings.

On Fox News late last month, Graham said he might propose a constitutional amendment because birthright citizenship has become a magnet for illegal immigration. "To have a child in America, they cross the border, go to the emergency room, have a child and that child is automatically an American citizen," he told host Greta Van Susteren. "That shouldn't be the case. That attracts people here for all the wrong reasons."

Amending the Constitution is a difficult task. Some who support curbing birthright citizenship argue that the 14th Amendment has been misinterpreted and that the issue could be dealt with more simply by passing a law or through the courts.

Groups that study immigration trends say the number of "birth tourists" to the United States is relatively small, perhaps a few thousand a year. The number of U.S. citizens born to illegal-immigrant parents is believed to be much higher; there were about 4 million such children living in the United States in 2008, according to the Pew Hispanic Center.

"This is a symptom of the larger problem of illegal immigration in this country," Jenks said. "It is an important issue. This is part of our identity as a nation, and we're the only industrialized country that has not changed its birthright citizenship laws."

More troubling to some is that illegal immigrants often further root themselves in U.S. society by having American children, their plight often winning the sympathy of the public. In one widely publicized case in 2007, a Mexican woman barricaded herself and her 8-year-old son, who was a U.S. citizen, inside a Chicago church in an unsuccessful attempt to avoid deportation.

Immigrant rights advocates say birthright citizenship is beneficial to society because it promotes assimilation, and that revoking that right could create generations of residents who reside in the country illegally.

"It's puzzling that they would propose this, because it would add to the undocumented population," said Bill O. Hing, a professor at the University of San Francisco School of Law who has represented undocumented immigrants. "I really think they lose sight of who these children are and what they become. . . . They very quickly become assimilated."