WASHINGTON -- Republican Sens. David Vitter (La.) and Rand Paul (Ky.) are seeking to deny birthright citizenship to the children of illegal immigrants by changing the U.S. Constitution.

The Supreme Court has consistently held that the Fourteenth Amendment grants automatic citizenship to those born on U.S. soil, but Vitter and Paul said Thursday that right should not extend to the children of undocumented parents. They introduced a congressional resolution that would amend the Constitution and close what they call a "loophole."

It's incorrect to assume "the 14th Amendment confers birthright citizenship to the children of illegal aliens, either by its language or intent," read a statement from the Senators. "This resolution makes clear that under the 14th Amendment a person born in the United States to illegal aliens does not automatically gain citizenship."

The last constitutional amendment was passed in 1992, more than two centuries after it was submitted by Congress to the states. Most successful amendments have been enacted within a few years of being proposed, but they are rare. In the past 140 years, only 12 have become law.

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Ed. note: This story has been updated to clarify that this is an attempt to amend the Constitution itself, not merely a legislative resolution to suggest an interpretation of the document.

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The debate over interpretation of the Fourteenth Amendment hit a fever pitch in Congress last summer, when Sen. Lindsey Graham (R-S.C.) said undocumented immigrants come to the country to "drop and leave" their children and Rep. Louie Gohmert (R-Texas) said he feared "anchor babies" would be used by al Qaeda to raise radicals with American passports.

At the state level, legislation similar to the Vitter-Paul resolution is already underway. Arizona state Sen. Ron Gould (R) and state Rep. John Kavanagh (R) agreed to unveil bills jointly on Thursday that would limit citizenship to children with at least one parent who "has no allegiance to a foreign country." The bills have already garnered support from state Senate President Russell Pearce, the author of Arizona's controversial 2010 immigration law SB 1070. A number of other state lawmakers plan to introduce similar legislation.

Because states administer birth certificates, state legislators claim they have the right to change how citizenship is defined under the Fourteenth Amendment. This could, however, create a patchwork system of citizenship criteria.

Led by Pearce and Republican Pennsylvania state Rep. Daryl Metcalfe, some state lawmakers formed the 14th Amendment Citizens Model Committee to draft such laws this past fall.

In some states, the goal is for the law to be challenged. Texas state Rep. Leo Berman (R) said in October he hoped his bill would lead to a Supreme Court case in which the court could reassess how birthright citizenship is defined.

But most legal scholars say the Court has already issued rulings on the amendment, which was adopted in 1868 to overturn the Dred Scott ruling and affirm citizenship for freed slaves and others of African descent. The Court ruled in 1898 that a child born in the United States to non-citizens was a citizen under the law.

If these efforts to change the Fourteenth Amendment came to fruition, it could significantly increase the number of immigrants considered to be in the U.S. illegally, which currently stands at an estimated 11 million people. In 2008, about 340,000 babies, or 8 percent of the babies born in the United States that year, were born to illegal immigrants, according to a Pew Hispanic Center study released last year.