The federal government is trying to take away citizenship from naturalized Americans at a pace not seen in decades — and its most prominent target so far is a sitting member of Congress.
The investigation into Rep. Ilhan Omar, D-Minn., is aimed at revoking her citizenship and deporting her, if investigators can prove she or her relatives lied to immigration authorities, two people familiar with the matter said on condition of anonymity, as they were not authorized to discuss the investigation.
Investigators searched Omar's home in Washington on Oct. 12 and issued subpoenas to her relatives. The probe, one official said, is focused on two questions. One is whether the family misrepresented Omar's age, and the other is whether her late father, Nur Omar Mohamed, concealed details of his military career.
A former Justice Department attorney and four legal scholars who study denaturalization, the legal process by which the government revokes U.S. citizenship, said the case looked unlike any they've seen.
"Nothing about this case is a normal denaturalization case," said Amanda Frost, a professor of law at the University of Virginia. "I think it's about punishing a political enemy."
Omar, who was born in Somalia, denied the Trump administration's accusations and called the probe "an authoritarian move to silence an opponent right before an election."
The government can try to revoke citizenship through a criminal case or a civil one.
Criminal cases carry a 10-year statute of limitations, require proof beyond a reasonable doubt and give defendants a jury and a lawyer. In civil cases, there's no time limit, jury or right to a court-appointed lawyer.
"So procedurally, it's just easier for the government to win a civil case than it is to win a criminal case," said Cassandra Burke Robertson, a professor of law at Case Western Reserve University who has written extensively about such cases.
The government generally takes one of two approaches, said Daniel Kanstroom, a law professor at Boston College. It can argue the person was never eligible, for example, because a crime committed before naturalization meant they lacked the good moral character the law requires. Or it can argue the person lied or concealed something.
He noted the second kind is much harder to win, because the government must prove the misrepresentation was willful and the material was serious enough that it would have led officials to find the person ineligible.
Such cases often take years. Losing citizenship does not mean automatic deportation. People revert to their earlier status, usually a green card, and the government must start separate proceedings in immigration court to remove them.
In the first half of the 20th century, the government routinely stripped citizenship from anarchists, suspected communists and labor leaders, Frost said. In 1967, the Supreme Court shut most of that down, ruling that citizenship could be taken away only in cases of fraud or error in the process.
Robertson said the court warned that using denaturalization in a political sense "is just flatly incompatible with democracy."
The ruling also determined that a naturalized U.S. citizen who commits a crime can be prosecuted like anyone else "but you can't lose your citizenship for conduct after your naturalization," Frost said.
At the heart of that protection, she said, is an idea the Supreme Court returned to repeatedly: that, in a democracy, "the people choose their government. The government doesn't choose the people."
After the ruling, administrations of both major parties filed about a dozen cases a year, and prosecutors were "very careful about bringing them," Kanstroom said. Because denaturalization cases are costly and hard to win, the government saved them for sure bets and the worst offenders, including Nazi war criminals, terrorism suspects and people who hid serious crimes.
Because of how selective prosecutors were, they won the vast majority of cases, he added.
President Donald Trump's first administration tried to expand the practice but filed on average 25 civil cases a year, according to the nonpartisan Migration Policy Institute. Under President Joe Biden, the number fell to about four a year, data from the Transactional Records Access Clearinghouse at Syracuse University shows.
Research by Irina Manta, a law professor at Hofstra University, found 168 cases in the courts during the first Trump administration and 64 under the Biden administration.
In June 2025, the Justice Department told its lawyers to "maximally pursue" denaturalization. It later set a goal of 250 cases by this month.
Since Trump returned to office, the government filed 196 civil denaturalization cases, according to a database maintained by Democracy Forward, a legal advocacy group that sued the administration for records on the effort. The database covers filings through Oct. 8.
On Oct. 5, the Justice Department announced it seeks to revoke the citizenship of 40 people in cases filed from late August through early October. It said the cases involved people accused of concealing crimes, immigration fraud, marriage fraud and using false identities. Attorney General Todd Blanche said they included people convicted of offenses ranging from espionage and money laundering to sexual crimes against minors.
Of the 196 cases filed, 20 were closed and the rest are pending. Twenty-three people had their citizenship revoked.
Those early wins may not last, experts said. Many of the newer cases accuse people of lying on their applications, which Kanstroom said is the hardest kind of case to prove.
Omar became a citizen in 2000 at age 17 through her father's naturalization, a route open only to children under 18. Investigators are focused on her age, a person familiar with the matter said. Proving she was older would be difficult, Kanstroom and Roberston said.
The statute of limitations on criminal naturalization fraud expired long ago, the experts said, so an attempt to revoke Omar's citizenship would have to be a civil case.
That makes the search warrant, a tool of criminal investigations, striking. Robertson said she had never seen one used in a civil denaturalization case.
