President Trump has threatened to use an executive order to override what has long been accepted as the constitutional right of birthright citizenship — the granting of automatic citizenship to any child born on U.S. soil regardless of their parents’ immigration or citizenship status.

It’s not clear if Trump is sincere with this promise or if this amounts to little more than a last-minute ploy to rile up his base before the important midterm elections. Any executive order or act of Congress (U.S. Sen. Lindsey Graham, R-S.C., has promised to introduce legislation) would surely be challenged in the courts.

But to the parents of millions of children of unauthorized immigrants who were granted birthright citizenship, and the countless more who may be born in the months ahead, this is no doubt worrisome rhetoric.

A 2016 report by the Migration Policy Institute estimated that New Jersey was home to 128,000 children between 2009 and 2013 who were born in the United States to unauthorized immigrants. That represented 76 percent of all children of immigrants living illegally in the state.

New Jersey had the 8th highest number of children of unauthorized immigrants in the country. In neighboring states, New York was home to 293,000 children of unauthorized immigrants, 78 percent of whom were granted birthright citizenship. And Pennsylvania was home to 46,000 such children, 69 percent of whom were citizens.

Exact numbers of unauthorized immigrants do not exist. The American Community Survey, an offshoot of the Census, tallies non-citizens, but doesn’t differentiate between those who are legal or not. The Migration Policy Institute came up with its own formula, using national estimates of other surveys that do take note of legal status, combining them with the more detailed American Community Survey reports to determine their state-by-state estimates.

Pew Research Center’s own estimates put the number of unauthorized immigrants in New Jersey in 2014 at 500,000.

Gov. Phil Murphy on Tuesday reacted to Trump’s threat, saying the Republican wants to “overstep his authority.”

“As a nation of immigrants, we will not stand for his attacks on our fundamental values.”

Trump and supporters of his argument believe that birthright citizenship is not enshrined in the 14th Amendment. Section 1 of the amendment 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. “

To the Trumpian reading of the clause, the words “and subject to the jurisdiction thereof” are key. They believe this would not apply to unauthorized immigrants.

The amendment was adopted after the Civil War. It overturned the U.S. Supreme Court’s Dred Scott decision, which had held that former slaves and their descendants could never be citizens.

The birthright citizenship interpretation of the clause as it applies to immigrant-born children dates to the Supreme Court’s 1898 decision in U.S. vs. Wong Kim Ark. The court ruled that a child born to Chinese parents in California was a citizen even though Chinese immigrants were prohibited by law from ever becoming citizens.

But opponents of birthright citizenship say that case is not entirely analogous to unauthorized immigrants of today because even though Chinese immigrants back then were barred from citizenship, they still had the legal right to live and work in this country.

Still, subsequent court rulings have upheld birthright citizenship for unauthorized immigrant children.

In the Supreme Court’s 1982 decision in Plyler v. Doe, which was over the question of whether states were obligated to provide free public education to children of unauthorized immigrants, even the dissenting justices who believed that Texas’ law against unauthorized immigrants was not unconstitutional agreed that under the 14th Amendment, unauthorized immigrants were "within the jurisdiction" of the states they were in. The overturned Texas law, furthermore, did not affect children born in this country to unauthorized immigrants.

In recent decades, immigration hardliners have set their sights on birthright citizenship. During the 2016 campaign, Trump used the term "anchor babies" to conjure the image of immigrant women flocking to our shores to give birth.

There's at least a modicum of truth to that. In 2016, NJ Spotlight exposed a New Jersey hospital's questionable practice of marketing to Russian-national women to give birth at Meadowlands Medical Center so that their children could become automatic U.S. citizens. The hospital's Russian-language website — which was taken down after reporters started asking questions — even promised to take care of citizenship and visa paperwork for a fee.

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