While most constitutional scholars think ending birthright citizenship would require a constitutional amendment, the opposite viewpoint is some credibility in conservative legal circles. Pepperdine Law professor Douglas Kmiec told ABC News that there is a "better than plausible argument" that Congress has authority under Sec. 5 of the 14th Amendment to end birthright citizenship through legislation.
"It is my study of the matter," said Kmiec, "that those who wrote the 14th amendment intended those words ("the jurisdiction thereof") to mean not owing allegiance to anybody else -- that is, subject to the complete jurisdiction of the United States, not simply to the laws of the United States or subject to the jurisdiction of the court."
Kmiec, who served as a constitutional legal counsel to former Presidents Reagan and Bush, said that someone who enters the U.S. illegally, and has not renounced the citizenship of the country from which he or she has emigrated, is not subject to the complete jurisdiction of the United States.
Gingrey shares Kmiec's assessment that Congress likely has the power to end birthright citizenship through legislation. The Georgia Republicans says, however, that he would like to see Congress take that step regardless of whether it required a constitutional amendment, and he is encouraged by Romney's recent comments.
I would be "pleased to know that he would stand strong against that and eliminate birthright citizenship," said Gingrey.
When it comes to McCain's efforts to offer a path to earned citizenship for the 12 million illegal immigrants currently in the United States, Romney has worked to brand his chief rival as a proponent of "amnesty."
Speaking of McCain, Romney recently told Nightline, "His immigration, bill, I think, is an amnesty-style program that I don't support."
By flirting with an end to birthright citizenship and by portraying earned legalization as "amnesty," Romney is departing not only from the course set by McCain but also from that of President Bush who, since his days as governor of Texas, has worked to moderate the GOP's image on immigration and to court Hispanic voters.
In a March 26 memo to members of the Republican National Committee, former Bush strategist Matthew Dowd maintained that voters "don't consider granting legal status to those already here amnesty." Dowd also urged RNC members to pursue a "comprehensive" solution to immigration with an eye on the country's burgeoning Hispanic population.
Romney's hardline on immigration isn't likely to attract Hispanic voters, but it has struck a cord with some of his backers in the House.
"He is strong on border security, and he is against amnesty," Gingrey told ABC News, "and that is certainly part of the reason why I am so enthusiastic in my support for Gov. Romney."
ABC News' Matthew Zavala contributed to this report.