Flags await the more than 220 people from more than 40 countries participating in the Fiesta of Independence Naturalization Ceremony at South Mountain Community College in Phoenix on July 4, 2018. (Carolyn Van Houten/The Washington Post)
Martha S. Jones is the SOBA presidential professor of history at Johns Hopkins University and author of "Birthright Citizens: A History of Race and Rights in Antebellum America."

I expected to spend this year — the 150th anniversary of the 14th Amendment — glorying in its achievements.

Instead, I’m defending it from attack.

As much as anyone, I anticipated the arrival of July 9, 2018 — the day that marked 150 years since the 14th Amendment made birthright citizenship part of the Constitution. I’ve just published a book, “Birthright Citizens,” that explains how, for decades before the 14th Amendment’s passage, African American activists promoted themselves as members of the nation by virtue of their birth on U.S. soil.

I had not anticipated, however, that the amendment’s anniversary would coincide with a rising tide of opposition to birthright citizenship. Perhaps I should have seen it coming — I follow the phrase “14th Amendment” on Twitter, where over the past year there have been “calls” variously for its repeal, overturning or recall. I generally dismissed these as outbursts from an uninformed fringe that was naive about what it would really take to change the Constitution or alter the course of its interpretation.

Yet these voices share an important touchstone: Donald Trump. As far back as November 2015, then-candidate Trump proposed that Congress should undo the protections that the Constitution extends to the children of unauthorized immigrants born in the United States. Even Fox News’s Bill O’Reilly, sympathetic to the candidate’s critique of birthright citizenship, appeared taken aback by Trump’s lack of fidelity to a conventional view of how the Constitution can be amended, which does not include presidential fiat.

Today, though, the president’s ideas about birthright citizenship should not be dismissed as merely naive or ill-informed. Under his direction, the Justice Department and Immigration and Customs Enforcement officials are pressing the rule of law to its constitutional limits, if not beyond, when it comes to immigration policy. The likely appointment of yet another U.S. Supreme Court justice is on the horizon, making a new and unprecedented interpretation of the 14th Amendment possible.

The amendment’s vulnerability turns, in part, on its clause that exempts from birthright status people who are not otherwise subject to U.S. jurisdiction. Historically, this clause has been understood to exempt the children of foreign diplomats born in the United States from citizenship. Today, the same phrase is said by some to exclude the children of unauthorized immigrants from citizenship, even when they are born in the United States.

This isn’t the first time that there have been efforts, driven by racism, to use this clause to limit citizenship. In 1898, the Supreme Court heard the case U.S. v. Wong Kim Ark; U.S. officials argued that the son of Chinese immigrants, parents who could not themselves become naturalized citizens, was not a birthright citizen. Wong Kim Ark, it was argued, had inherited a fidelity to the Chinese emperor that his birth on U.S. soil could not extinguish. But the court disagreed, reading the 14th Amendment plainly: A person born on U.S. soil was a citizen of the United States, even if his parents never could be.

And yet, we should not be too reassured by this precedent from more than 100 years ago. A 21st-century court might distinguish between Wong’s parents who, though not citizens, were legally in the United States when he was born, and the children of those who are today here without authorization.

The popular groundswell that is demanding an end to birthright citizenship may not have arrived at well-thought-out theories of constitutional revision. But perhaps they need not do so. They have fellow travelers in the respectable circles of politics and academia, who are calling birthright citizenship into question in the pages of law reviews, magazine articles, scholarly books and op-ed pages. Many of these varied thinkers share an abhorrence of unauthorized immigrants and their children who are born in the United States and have been, until this point, deemed birthright citizens.

Some argue that the status of children born in the United States to unauthorized immigrants should be determined by Congress rather than the Constitution. Legal scholar Peter Shuck at Yale and political scientist Rogers Smith at the University of Pennsylvania have long made this argument, fully set forth three decades ago in their 1985 book “Citizenship Without Consent: Illegal Aliens in the American Polity.” Early this summer, Shuck and Smith reiterated this view for readers of National Affairs in an article titled “The Question of Birthright Citizenship.” They were outliers in 1985, but today they are in sync with the president and his base.

And his advisers: This week, Michael Anton, a self-described lecturer and research fellow at Hillsdale College and former national security official in the Trump administration, took to the op-ed page of The Washington Post to malign birthright citizenship. In a piece titled “Citizenship Shouldn’t be a Birthright,” Anton endorsed the view that reading birthright into the 14th Amendment’s Section 1 is not only wrong, but “an absurdity — historically, constitutionally, philosophically and practically.”

Yet as a historian and a lawyer — Anton is neither — I can assure you he is wrong. The birthright principle is plainly spelled out in Section 1 of the amendment: “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.” A constitutional innovation in 1868, it affirmed what black Americans had long asserted, that they — and all persons born in the United States — were citizens of the United States. Such a provision was necessary given the racist 1857 ruling in Dred Scott v. Sanford, which said no black person could be a citizen of the United States. The Supreme Court in 1898 was asked whether birthright also extended to the children of Chinese immigrants, whose parents could not themselves become citizens due to another racist ruling/law that barred Chinese immigrants from citizenship. The answer was yes.

So birthright has been affirmed, again and again, ensuring that no matter how racist the regime, the Constitution grants citizenship to all people born in the United States. The 14th Amendment transformed our governing text into a document that protects those born in the United States from arbitrary and politically motivated bars to citizenship, including race, religion and party affiliation. The 14th Amendment guarantees that no American will be subject to a test of patriotism, wealth or health. At birth, Americans are incorporated into the body politic and invited to take full part in the governance and the future of our democracy.

It is time to understand the 14th Amendment, and then defend it. Its 150th anniversary gave the nation an opportunity to celebrate the constitutional revolution that followed the Civil War and emancipation. Today, it is time to fully embrace the vision and the force of that revolution in our own lives. It is not a time for nostalgia, self-congratulation, or overconfidence. Instead, the rising calls to repeal birthright citizenship demand that we equip ourselves for the debate that is on the near horizon.