Everything You Need to Know About Birthright Citizenship and the 14th Amendment

(Bloomberg) -- Millions of people owe their rights as Americans to being born in the U.S., thanks to a principle known as birthright citizenship. President Donald Trump, who has made a priority of making it harder for foreigners to enter the country, wants to narrow or even eliminate this path for U.S.-born children with parents who are citizens of another country. Defenders of the practice may have the U.S. Constitution on their side.

1. What is meant by ‘birthright citizenship’?

The 14th amendment to the U.S. Constitution, adopted in 1868 and intended to clarify the post-Civil War status of former slaves, begins, "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." That has been taken to mean that being born on U.S. soil -- even to parents who are just passing through -- guarantees American citizenship to the child.

2. Has this been challenged before?

Many times, especially since the phrase "subject to the jurisdiction thereof" left room for debate over who exactly should qualify for this right. In an 1898 decision, the Supreme Court ruled that a child born in the U.S. to Chinese parents who "have a permanent domicil(e) and residence in the United States, and are there carrying on business, and are not employed in any diplomatic or official capacity under the Emperor of China, becomes at the time of his birth a citizen of the United States." Critics of birthright citizenship say that shouldn’t apply to immigrants living in the U.S. without proper authorization. Some members of U.S. Congress have been trying for years to withhold birthright citizenship from children with two unauthorized parents.

3. What does Trump say?

As a candidate, he said babies born on U.S. soil to parents who are not in the country legally shouldn’t have American citizenship. He called them "anchor babies" because once they become adults, they can petition for their parents to gain legal residency in the U.S. As president, Trump now says he will sign an executive order ending birthright citizenship for babies of non-citizens and unauthorized immigrants born on U.S. soil.

4. Can he do that?

Not without a fight. In general, changing the U.S. Constitution requires an amendment that passes Congress by a two-thirds majority and then gets ratified by at least 38 of the 50 states -- a high bar. Trump doesn’t see that as the only route. "It was always told to me that you needed a constitutional amendment. Guess what? You don’t," he said in an interview with "Axios on HBO." But any attempt to change the citizenship process by presidential order -- or even by standard congressional lawmaking -- would surely prompt a legal challenge.

5. How many people get to be U.S. citizens this way?

The Migration Policy Institute estimated in 2015 that there were 4.1 million children (under age 18) who at birth had both U.S. citizenship and at least one unauthorized immigrant parent -- meaning they potentially could owe their citizenship solely to the birthright provision (unless their other parent was American). The Pew Research Center estimated that 275,000 babies were born to unauthorized-immigrant parents in 2014, or about 7 percent of the 4 million births in the U.S. that year.

6. Is the U.S. alone?

European countries require a period of residency before bestowing citizenship on those born to foreign parents. But many countries in the Americas, including Canada, Mexico, Brazil and Argentina, have U.S.-style birthright citizenship.