In a highly unusual step, federal agents this week aggressively intensified their investigations into Democratic Rep. Ilhan Omar of Minnesota, weeks before she stands for reelection in her home district. 

The Department of Justice on Tuesday subpoenaed relatives of Omar’s family members, including her sister Sahra Noor, according to The New York Times. The grand jury subpoenas were issued shortly after a raid of the lawmaker’s residence in Washington, D.C. on Monday. 

The judicial search warrant, which is under seal, was executed by Homeland Security Investigations, the investigative branch of Immigration and Customs Enforcement. Although the Department of Justice did not provide any more details of the investigation, multiple outlets, citing anonymous sources, reported that the search stemmed from Omar’s immigration paperwork, which was filled out by her late father when she was a child. 

Prior to the investigation, multiple Trump Administration officials have accused Omar of immigration fraud without presenting any evidence. In a podcast interview in March, Vice President JD Vance said the White House was exploring “legal remedies” to her alleged immigration fraud. Last month, Homeland Security Secretary Markwayne Mullin said the investigation into Omar was “ongoing” and dismissed efforts to frame the case as political retribution.

“If we actually move a case forward, it’s not a political case. It’s actually a case because they did things wrong,” Mullin said during the interview with right-wing podcaster Benny Johnson. 

Omar, who has long denied the allegations, condemned the raid on her home as “political intimidation” and said she will “not be silenced.” 

President Trump, along with many MAGA Republicans, has repeatedly floated the idea of revoking Omar’s citizenship, a process also known as denaturalization, and deporting her. 

But legal and immigration experts tell TIME that denaturalizing a U.S. citizen is a rare and difficult process, one that requires federal authorities to clear a high bar in front of a federal judge. Here’s what to know about how the process works. 

How does denaturalization work?

Stripping someone of their citizenship is a more arduous legal process than most other immigration efforts that involve the courts. Deportation proceedings, for instance, are initiated by ICE agents under the Department of Homeland Security and are then approved by immigration judges who are hired and work within the Department of Justice. The denaturalization process, on the other hand, must be approved by an independent federal judge, who evaluates the request by a higher standard.  

All denaturalization efforts begin at DOJ. In order to revoke a naturalized person’s citizenship, a DOJ lawyer must decide whether to file a civil or a criminal petition in court. Yuripzy Morgan, an attorney and host of Free Range National podcase, said a civil complaint does not have a statute of limitation, whereas a criminal complaint has a statute of limitation of 10 years and must clear a much higher legal bar. 

“For civil denaturalization, the government has to show that there is clear, convincing, and unequivocal evidence that the person in question obtained their naturalization either illegally, or they willfully misrepresented a material fact, ” Morgan says. She stressed that simply having an error in an immigration document doesn’t mean that a judge is going to approve stripping a person of their citizenship. 

For a criminal denaturalization conviction, the federal government must show “proof beyond a reasonable doubt” that the individual knowingly obtained citizenship through fraud, which is the highest legal standard of proof required to secure a criminal conviction. In 2017, the Supreme Court unanimously ruled in Maslenjak v. United States that only an illegal act that played a role in a person’s citizenship application could lead to criminal denaturalization, further narrowing down the scope of such efforts. 

Omar’s father filled out and submitted her citizenship application on her behalf when she was 17. It is unclear what evidence, if any, the federal government has to show that anything in the application was fraudulent, or that Omar or her father intentionally misrepresented anything in that application. 

Andrew Arthur, a former immigration judge and a resident fellow at the Center for Immigration Studies, pointed out that even after someone gets denaturalized, a deportation is not guaranteed. The person would still be able to retain their previous legal immigration status until a final order of removal is issued to the person by ICE.

“If they had a green card before they naturalized, e

ven after they get denaturalized, they are going to have a green card,” Arthur says. 

How did Rep. Omar get naturalized as a U.S. citizen?

According to Omar’s House biography, Omar and her family fled her home country Somalia when she was eight. The family eventually sought asylum in the United States in 1995. She told The New York Times that she became a U.S. citizen in 2000 when she was 17. 

At the time Omar went through the process, federal law allowed immigrants under the age of 18 to get naturalized as U.S. citizens if both of their parents had become U.S. citizens. The law was eventually replaced by a new law in 2001, which only requires one parent to become a citizen for the children to be naturalized. 

At the center of this investigation is whether Omar’s father, Nur Omar Mohamed, lied about her age in immigration documents so she could be eligible to derive citizenship through him, according to The Washington Post, which cited two unnamed sources. 

According to Arthur, the former immigration judge, if Omar was 18 at the time of the naturalization application, she may have been able to apply for her citizenship on her own after having a valid green card for five years. 

The allegations regarding Omar’s citizenship gained attention among conservative activists and commentators starting in 2019, when Omar became a member of Congress. Shortly after her election, Omar’s staff sought to change her official birth year in public records from 1981 to 1982, according to multiple outlets.

How often does the U.S. government strip people of their citizenship?

Despite the renewed push from the second Trump administration, denaturalization remains an exceedingly rare legal process. According to the Migration Policy Institute, a Washington, D.C.-based think tank, an average of 11 denaturalization cases were filed per year between 1990 and 2017.