Birthright citizenship flows directly from the first sentence of the first section of the 14th Amendment to the United States Constitution which states:
All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside.This dove tails with the first sentence of the second section of the 14th Amendment which provides that:
Representatives shall be apportioned among the several states according to their respective numbers, counting the whole number of persons in each state, excluding Indians not taxed.The sole qualification to birthright citizenship, “and subject to the jurisdiction thereof” excludes children of foreign citizens with diplomatic immunity, and Indian tribes not subject to U.S. taxation (a class of persons which no longer exists as a result of The Revenue Act of 1924 (43 Stat. 253) (June 2, 1924), also known as the Mellon tax bill and the Indian Citizenship Act of 1924 (43 Stat. 253, Ch. 233 (1924) which subjected all Native Americans in the United States to federal income taxation and granted all Native Americans in the United States U.S. citizenship).
The definition of citizenship immediately prior to the adoption of the 14th Amendment in the United States was narrower and provided in 1866 that:
[A]ll persons born in the United States and not subject to any foreign power, excluding Indians not taxed, are hereby declared to be citizens of the United States. . . .This definition was expanded by the 14th Amendment. Rogers v. Bellei, 401 U.S. 815, 829 (1971). The 14th Amendment constitutionalized birth right citizenship, with the express purpose of not allowing it to be modified by statute. Rogers v. Bellei, 401 U.S. at 829-830. The case law under the “subject to the jurisdiction thereof” clause has largely freed it of any ambiguity or wiggle room to remove citizenship for people born in the United States without a constitutional amendment.
The only way to deprive children born in the U.S. to non-citizen parents of U.S. citizenship without a U.S. Constitutional Amendment is to grant their parents diplomatic immunity, both civil and criminal. Few people concerned about illegal immigration would be willing to take that step to achieve that end.
As a practical reality, the super-majorities necessary to eliminate birth right citizenship for persons born in the United States by constitutional amendment pursuant to Article V do not exist and will not exist for the foreseeable future.
The United States citizenship laws allow some people to be citizens at birth even though they are not born in the United States (e.g. the “Superman” exception for children found wandering around without parents in the U.S. without known paternity as toddlers or younger who are U.S. citizens unless proved otherwise by the time that they attain the age of eighteen). Those provisions are subject to modification by statute and to the extent that they are ambiguous can be interpreted by federal regulation.
UPDATE: March 11, 2015.
A Congressional Research Service report from 2005 acknowledges the existence of the view that a statute could end birthright citizenship, notwithstanding the clear language of the 14th Amendment and multiple U.S. Supreme Court rulings to the contrary, but does not adopt, endorse, or credit that view which has no support from any actual court rulings.