For decades, the right to be a U.S. citizen by being born on American soil was considered an almost untouchable principle. This guarantee, known as birthright citizenship, has been part of the legal identity of the United States for more than 160 years. Today, however, it faces its moment of greatest uncertainty.

On his first day of this new term, President Donald Trump signed an executive order seeking to eliminate automatic citizenship. The impact is not minor: if fully applied, the measure would affect thousands of babies born to undocumented parents and also the children of those who are in the country on temporary visas. The controversy quickly reached the courts.

Although several federal courts blocked the order with injunctions, the Supreme Court last week decided to lift those nationwide injunctions, without yet ruling on the constitutional validity of the initiative. That decision, seemingly technical, opens the door for the order to come into force unevenly across the country: while in 22 states that did file lawsuits it will remain provisionally suspended, in another 28 states—including Texas, Arkansas, and Mississippi—it is set to take effect in just one month, unless a new legal offensive succeeds.

The confusion is widespread. What will happen to children born in those states? Will they have a U.S. passport or be left in a legal limbo? According to experts consulted by The New York Times, the situation could lead to cases of statelessness, especially if the parents’ countries of origin do not automatically recognize citizenship by descent. Mexico, Brazil, and Poland, for example, would allow the child to acquire the parents’ citizenship, but other countries have no such provisions.

The legal debate is only beginning. By rejecting the nationwide injunctions, the Supreme Court suggested that the way forward for new litigation could be a class action that groups together all affected individuals. Organizations such as the ACLU and Democracy Defenders Fund are already mobilizing to certify these lawsuits before the 30-day deadline imposed by the Court expires. If this effort fails, the Trump administration could start enforcing the measure in dozens of states.

Meanwhile, questions remain unanswered. Attorney General Pam Bondi declined to specify which authorities would verify the parents’ immigration status or whether hospitals would be required to participate in the process. It is also unclear what will happen to babies born to parents on temporary visas, such as H-1B holders or students. According to Professor Cristina Rodríguez of Yale Law School, these children would not obtain automatic citizenship and would be left with a derived, probably precarious status.

Even if the Supreme Court eventually declares the order unconstitutional, the damage would already be done. Thousands of children could have been deprived of essential rights, subjected to deportation, or denied access to health services. The process of retroactively recognizing citizenship would be complex and traumatic.

Stephen Yale-Loehr, a Cornell academic, warned that ending birthright citizenship would not only be a historic legal change but a scenario filled with unforeseeable consequences:

“The practical problems of ending birthright citizenship are both huge and unpredictable.”

The paradox is clear: a constitutional principle that guaranteed clarity and stability for generations of immigrants is now subject to a political and legal battle that is only just beginning. Meanwhile, thousands of families are waiting for decisions that could define their future in the United States. This story is just starting, and new, likely more controversial chapters are sure to come.