The Trump administration and its supporters have made numerous threats to revoke the citizenship of political foes who are naturalized citizens. But if the government tries to follow through, it will have an uphill legal battle.
Most recently, the calls singled out New York City Mayor-elect Zohran Mamdani, with the president’s allies on Capitol Hill demanding that the Justice Department “denaturalize and deport” him. President Trump himself — before last week’s chummy White House meeting — suggested Mamdani was a “communist” and “here illegally,” echoing rhetoric from the McCarthy era, when alleged communist sympathies were enough to cost a person their job or even get them deported.
Mamdani is one of nearly 25 million naturalized citizens currently living in the United States. The push to investigate Mamdani’s citizenship is the latest turn in the administration’s broader attempt to reinterpret what it means to be an American citizen — and remain one. Justice Department attorneys have been instructed to “prioritize and maximally pursue denaturalization proceedings.” Before that, the president issued an executive order attempting to end birthright citizenship, which is guaranteed by the 14th Amendment and more than a century of Supreme Court precedent.
Under the law today, the government may seek denaturalization proceedings either when naturalization is obtained illegally or disqualifying facts on citizenship applications are concealed. But throughout much of the 20th century, it was much easier to achieve.
More than 22,000 Americans lost their citizenship between 1907 and 1967 based on political affiliations, race, and gender, according to denaturalization scholar Patrick Weil. President Woodrow Wilson’s administration began denaturalizing German- and Asian-born citizens during World War I, along with anarchists and people who spoke out against the war. During World War II, a push for denaturalization of naturalized citizens from Germany, Italy, and Japan intensified. A primary target included members of the pro-Nazi German-American Bund for disloyalty and insufficient attachment to the principles of the Constitution.
After the war, the Second Red Scare took hold of a country fearful of domestic communism amid its emergence abroad. Sen. Joseph McCarthy of Wisconsin led witch hunts, with denaturalization often used as a tool against accused communists or sympathizers. Among those targets was Harry Bridges, an Australian-born, nationally known labor leader accused of being a communist, who faced an ultimately unsuccessful campaign to revoke his citizenship. The Supreme Court ruled in his favor, not once, but twice.
Throughout the 20th century, the Court’s jurisprudence evolved to protect naturalized citizens — even those with unpopular views during wartime — against efforts to strip them of citizenship. The Court established constraints on the government’s ability to revoke citizenship in a case challenging an attempt to denaturalize Russian-born William Schneiderman over ties to the Communist Party. The Court wrote, “We believe the facts and the law should be construed as far as is reasonably possible in favor of the citizen.” It also emphasized that citizenship should not be rescinded lightly: “[The United States] must sustain the heavy burden which then rests upon it to prove lack of attachment by ‘clear, unequivocal, and convincing’ evidence.”
A few years later, the Supreme Court warned against using denaturalization proceedings as a political weapon. “Ill-tempered expressions, extreme views, even the promotion of ideas which run counter to our American ideals, are not to be given disloyal connotations in absence of solid, convincing evidence that that is their significance,” the Court’s majority wrote. “Any other course would run counter to our traditions, and make denaturalization proceedings the ready instrument for political persecutions.”
In 1967, the Court found that under the 14th Amendment, the government cannot forcibly deprive a naturalized American of citizenship without the citizen’s consent, except when citizenship is “unlawfully procured.”
In the succeeding decades, denaturalizations declined significantly. Between 1990 and 2017, the Justice Department filed an average of just 11 cases per year. Only during the Obama administration did they climb, when new technology allowed the government to search decades of data for indicators of possible fraud. In 2016, the yearly average rose to 15. During the first Trump administration, the program expanded, increasing the average to 25 per year.
Yet the Supreme Court remained resistant to easing limits on denaturalization. In 2017, the Court unanimously ruled that citizenship was “unlawfully procured” only if the unlawful act, such as making a false statement, had a causal connection to the acquisition of citizenship. The Court wrote that a prosecutor should not be able to “scour her paperwork” and bring a charge because doing so would “give prosecutors nearly limitless leverage — and afford newly naturalized citizens precious little security.”
The second Trump administration is picking up where the last one left off, filing at least 25 cases in the first 10 months of 2025. Based on publicly available information, these cases are not obviously aimed at political viewpoints. But any attempt to use denaturalization as a political weapon will run into significant legal hurdles. The Supreme Court’s firmly established limits on the process are not only robust, but also deeply rooted in protections guaranteed by the 1st and 14th Amendments.
