In a strangely jolly introductory clip the news outlet Axios put out today (October 30) to tease its upcoming HBO show, President Donald Trump announced that he will pass an executive order that would end birthright citizenship, the constitutional guarantee that people born in the United States are automatically citizens. The immediate response throughout social and news media has been that the 14th Amendment protects birthright citizenship and is immune to executive orders. (You know, separation and balance of power and all of that.) But Princeton University law professor and author Imani Perry says it’s more complicated—and less secure—than many of us think. Here is Perry’s warning:

Almost every year I teach a class on the history of race and the law. An essential part of that class is the 1898 Supreme Court case, United States. v. Wong Kim Ark. Wong Kim Ark was the son of Chinese immigrants who, because of the Chinese Exclusion Act, could not become citizens of the United States. However, unlike his parents, Ark was born in the United States and asserted that he was a citizen due to the citizenship clause of the 14th Amendment which reads, “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…” The case is important in constitutional law because, in applying and interpreting the 14th Amendment, it firmly established the law of birthright citizenship.

This morning, it was reported that President Trump has plans to revoke birthright citizenship by executive order. This is yet another example of Trump’s willful ignorance, or his deliberate deception. Or both. After all, a president cannot revoke a constitutional protection by executive order. That isn’t how any of this works. Accordingly, many pundits have said we shouldn’t worry about this latest antic.

But the pundits shouldn’t be so blasé. Given the relatively minimal checks the House and Senate have placed on Trump’s unethical and even criminal behavior, we should expect that he will take steps to begin destroying birthright citizenship. Trump campaigned on that objective. He has proclaimed a thinly veiled White nationalism that reaches back into a long history of excluding people of color from citizenship, either literally or effectively. And the fact that there are mostly Latinx migrant children living in a tent camp detention center in Tornillo, Texas, right now should make us even more vigilant about his intentions. And we must not forget that immigration rights lawyers have decades of personal stories about how sometimes legal immigrants are illegally deported or have their green cards illegally taken by immigration agents. Vulnerable populations are always at risk of having their rights breached no matter how firmly established they are.

That said, if Trump did sign this executive order and attempt to enforce it, it would immediately trigger a spate of lawsuits charging that the president had violated the 14th Amendment. And what then? A signature priority of this administration has been to pack the federal courts with ultra-conservative—and in numerous instances clearly unqualified judges. While it seems unlikely that even the most conservative among them would overturn birthright citizenship, it is possible that if and when the case made its way to the Supreme Court, the Court could weaken or limit its enforcement with devastating impact. Moreover, regardless of what it rules the Court can’t force the president to adhere to its ruling. It has no military and no police, no enforcement power of its own. It depends upon the political branches. Sadly, the House and Senate have shown themselves to be weak protectors of freedom and justice in this political season. As the historian Martha Jones has shown in her brilliant book “Birthright Citizens,” history shows that it was a hard fought for right, one that is at once essential and fragile.

The truth is, we have a long history of exclusion from the robust protection of the 14th Amendment when it comes to people of color. Two well-known examples come immediately to mind: Plessy v. Ferguson (1896) which upheld segregation, and Korematsu v. United States (1944) which upheld the internment of Japanese Americans. Additionally, we were well into the 20th Century when the court finally held that Native Americans were included in birthright citizenship, when Congress finally allowed Asian immigrants to become naturalized, and when the courts finally began to protect African-American citizenship. The Constitution is a living entity. And while our judges value stability, they are consistently called to interpret it anew. This interpretation can go in many different directions. In recent years, from Standing Rock to Puerto Rico, we are witnessing systematic injustices that fly directly in the face of 14th Amendment protections without remedy for the aggrieved. All of this to say: Just because it is a right doesn’t make it a reality.

Furthermore, even if courts appropriately understood Trump’s prospective executive order to be a violation of the Constitution it would still have collateral effects. When the government sends the message that certain people are not qualified to be citizens it stigmatizes those people in numerous ways and legitimizes violence against them. It inhibits them from experiencing the full panoply of rights. Bigoted cultural attitudes, affirmed by those in positions of power, shape how law operates in peoples’ lives. They impact policing, immigration policy and practice, education, housing, and more.

If we are not vigilant our mantras of “never again” can easily slide into a world of “over and over again.”

Imani Perry is the Hughes-Rogers Professor of African American Studies and Faculty Associate in Law and Public Affairs at Princeton University.