Birthright citizenship is embedded in the 14th Amendment, ratified in 1868, which states: All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and the State wherein they reside.
The idea was to grant citizenship to recently freed slaves. But the 14th Amendment also forms the basis of the countrys longstanding policy of granting birthright citizenship to anyone born on American soil.
The birthright citizenship portion of the amendment was upheld by the Supreme Court in 1898 in the case United States v. Wong Kim Ark, which involved a man, Wong Kim Ark, who was born in San Francisco to parents who were citizens of China but legally living in the United States. (There was no such thing as illegal immigration at the time.) Some argue that while that settles the issue of whether the 14th Amendment grants citizenship to children born to parents in the country legally, it doesnt necessarily settle the issue regarding children born in the U.S. to parents in the country illegally.
The only other Supreme Court involvement on the issue is a footnote in a 1982 decision in the case Plyler v. Doe, which dealt with the issue of whether states must provide education to children not legally admitted into the United States. In that case, Justice William Brennan, writing the majority opinion in the 5-4 decision, stated that no plausible distinction with respect to Fourteenth Amendment jurisdiction can be drawn between resident aliens whose entry into the United States was lawful, and resident aliens whose entry was unlawful.
As a matter of practice, the U.S. government has interpreted the wording of the 14th Amendment to mean that children born in the U.S., even to parents who are in the country illegally, are deemed citizens. And most constitutional scholars believe it would require a constitutional amendment to change that. Constitutional amendments are hard to enact. They must be proposed by a two-thirds majority in both the House and Senate, and then need to be ratified by three-fourth of the states.