Unlike the recent suggestions of President Donald Trump, you cannot end birthright citizenship with an executive order. Or even a bill in Congress. So says the Constitution. But don’t trust this president or the next Congress to necessarily agree with the plain meaning of these words. Or future federal officials. Or even the federal courts. Because unbeknownst to most Americans, for more than a century all three branches of government have perpetuated an unconstitutional denial of birthright citizenship.

On Wednesday, the Trump administration will appear in federal court to defend the ability of the political branches to unilaterally restrict the Constitution’s guarantee of birthright citizenship. No, it will not be to defend an executive order or congressional statute denying citizenship to U.S.-born children of unauthorized immigrants. Rather, in Fitisemanu v. United States, the administration is defending the unconstitutional denial of birthright citizenship in U.S. territories before the U.S. District Court for the District of Utah. (Both authors are involved in the lawsuit.)

Many assume that the overwhelming bipartisan consensus condemning the constitutionality of Trump’s plan to restrict birthright citizenship by executive order or congressional statute makes such plans dead on arrival. Simply put, the original understanding of the Citizenship Clause requires recognizing all born on U.S. soil as citizens (the only narrow exceptions are for the children of foreign diplomats, enemy soldiers, or certain Indian tribes). An unbroken line of Supreme Court precedent agrees.

But America’s unsavory history of denying birthright citizenship in overseas U.S. territories offers a cautionary tale.

Today, the federal government labels people born in American Samoa as “non-citizens,” even though it has been a U.S. territory since 1900. Moreover, it holds that the citizenship of millions of Americans born in Puerto Rico and other territories is based on statute, not constitutional right, and could be rolled back by Congress.

Legal scholars across the ideological spectrum reject this view as a racist, anachronistic, and “unconstitutional exception … invented by administrators and legislators.”

Yet, here we are.

The problem began in 1899, when President William McKinley oversaw annexation of Puerto Rico, Guam, and the Philippines from Spain. In step with prevailing racial attitudes, he judged the native inhabitants unfit to be American citizens. So he acted unilaterally to deny them citizenship.

McKinley’s view—like Trump’s—was clearly contrary to well-settled understandings of the Citizenship Clause. Shortly after the 14th Amendment’s ratification, the Supreme Court explained the clause “put[] at rest” the proposition that “[t]hose who had been born and resided always in the District of Columbia or in the Territories, though within the United States, were not citizens.” After all, the chairman of the Senate Judiciary Committee explained during congressional debates over the Citizenship Clause that it “refers to persons everywhere, whether in the States or in the Territories.” (All emphasis ours.)

Americans shouldn’t casually dismiss the threat of a president or Congress redefining the Citizenship Clause to exclude disfavored groups.

But just as Trump is not swayed by the consensus on birthright citizenship today, McKinley’s administration was undeterred then.

Inevitably, the issue reached the Supreme Court. Its response should leave us feeling queasy.

In a 1901 case involving tariffs on oranges from Puerto Rico that had nothing to do with citizenship, key Justices nonetheless opined on the racial fitness of residents of the territories to be citizens. Justice Henry Billings Brown—the author of Plessy v. Ferguson—rejected birthright citizenship for territorial inhabitants’ “children thereafter born, whether savages or civilized.” Justice Edward Douglas White expressed concern about “bestowal of citizenship on those absolutely unfit to receive it.”

Three years later, the Supreme Court directly faced the question of citizenship. Immigration officials had excluded a Puerto Rican woman as an undesirable alien. She contended that Puerto Ricans were citizens; the federal government argued they were not. The Supreme Court blinked, expressly dodging the question of citizenship and declaring only that Gonzales was not an “alien.”

Every administration since has taken this as a wink and a nod that it need not recognize people born in overseas territories as citizens. Now, more than a century after McKinley carved an “unconstitutional exception” to birthright citizenship, federal law continues to classify people born in overseas U.S. territories as “non-citizen U.S. nationals” unless Congress says otherwise.

Next week a group of passport-holding, tax-paying Americans living in Utah who are labeled non-citizens because they were born in American Samoa will have their day in court. They will ask a federal judge to reject the idea that the political branches can redefine the Citizenship Clause.

We remain optimistic the courts will ultimately recognize that the Citizenship Clause means what it says when it comes to birthright citizenship in U.S. territories.

But this history offers an important lesson.

Americans shouldn’t casually dismiss the threat of a president or Congress redefining the Citizenship Clause to exclude disfavored groups. When political imperatives and racial hostility mix together, the Supreme Court cannot always be relied on to defend the Constitution’s guarantee of birthright citizenship.

Unilateral executive action narrowed constitutional birthright citizenship once before, and we are still living with the consequences.