The Trump administration claims thousands of noncitizens are on California’s rolls. How it found those names is a mystery

The Trump administration is pressuring California to disenfranchise thousands of people it claims are noncitizens after voting has already begun. But the administration has offered scant details on how it drafted a list of people it claims are illegally registered to vote in the Golden State.

For a central plank of the administration’s claim — that it used reliable methods when it identified roughly 20,000 people as noncitizens — the best answer federal agencies can offer is: Trust us.

But a close look at what we know about the administration’s pressure campaign against California and Los Angeles County — which has included threats to prosecute election officials — suggests it’s based on an opaque investigative process for gathering and analyzing the data.

A government whistleblower also has alleged the process is rife with errors. And on Wednesday, a federal judge halted some Department of Homeland Security operations that used much of the same data to identify alleged noncitizens in nine states, finding the agency’s “target lists” suffered from a “high likelihood of error.”

How exactly the administration compiled the list of alleged noncitizens registered to vote in California remains unclear. In court filings and letters to election workers, the Department of Justice (DOJ) has referred broadly to a system that cross-checks voters’ citizenship data across a wide variety of federal and commercial databases. 

The government’s most detailed description of the vetting process came in its request for a temporary restraining order barring California from counting ballots from the 20,000 people flagged.

According to that Oct. 19 filing, Immigration and Customs Enforcement’s Homeland Security Investigations (HSI) division “received what appeared to be the California voter roster for the general election of 2026.” The filing and supporting documents do not explain where or how HSI received or verified the roster’s accuracy. 

However, an internal HSI report from June obtained by Democracy Forward indicated it may have received some California voter data from DOJ. 

As part of its review process, HSI hands the data over to U.S. Citizenship and Immigration Services (USCIS), which “begins its process by enhancing the voter data it receives through a reliable third-party data analytics and investigative platform,” according to court documents.

The review process compares voter information to Department of State and Social Security Administration data to remove verified American citizens or voters who may have died. From those initial results, USCIS’ Fraud Detection and National Security Directorate (FDNS) investigators manually check the records to identify potential noncitizens who may be registered to vote.

“As I understand, FDNS developed a model that uses information from the voter roll and combines it with information from a reliable third-party data analytics and investigative platform to learn more about the individuals,” according to a declaration from Eric McLoughlin, assistant director for HSI’s Cyber and Operational Technology section, that was included with the temporary restraining order request. 

That suggests the administration could be using an AI model to sift the voter information.

After that, HSI can use “data matching across multiple authorized data sources and consolidate disparate records,” the declaration says. Those records are sent to HSI field offices to pursue prosecutions. 

That’s the review process that the Trump administration used to compile the list of 20,000 noncitizens it claims are registered to vote in California. However, in court documents, the government calls that “the floor of potential noncitizen California voters” and suggests it may have identified another 17,000 people who might be illegally registered to cast ballots in the state.

Where did the California data come from?

One unanswered question is how the DOJ originally obtained California’s public voter rolls to initiate DHS’s investigation. 

According to court documents, HSI forwarded the purported California voter register to USCIS and FDNS for review “on or around May 8, 2026,” meaning the DOJ possessed a portion of the state’s registration list around five months ago.

“The roster appeared credible enough for our office to initiate our investigative processes in accordance with our standard operating procedures,” McLoughlin said in his court declaration.

Unlike many other states, California heavily restricts access to its voting records. In fact, its election code explicitly bars companies from obtaining, collecting and selling election-related data.

While the state’s public roll is available for purchase, only certain people, such as political candidates, can buy the roll, and the secretary of state must approve all purchases. Moreover, all buyers must explicitly say how they intend to use the data and swear under penalty of perjury that they are telling the truth.

At most, the DOJ disclosed in its lawsuit that California’s voter roll is available for purchase. It did not say if it purchased the roll from the state directly or if it obtained it from an undisclosed source.

The internal HSI report from June indicated it had “ingested” 50.6 million state voting records it received from DOJ and was processing the data from “priority states” including California.

That same report also said Heather Honey, a longtime election conspiracy theorist who is now a senior DHS official, obtained another 48.4 million records from “independent sources of information.”

The Trump administration’s description of how it identified the 20,000 voters is strikingly similar to an intensive and deeply flawed DHS probe for illegal voting that a government employee detailed in a whistleblower report last month.

The whistleblower alleged that agents from the same DHS subagenices involved in California probe were knowlingly flagging U.S. citizens as “unlawful voters.” The official also said agents were using people’s sensitive personal data to access individual voting registration files through state election portals, potentially in violation of state privacy laws. 

States question administration’s methods

President Donald Trump has baselessly claimed for years that noncitizens voting is a widespread problem when in reality it’s something that rarely occurs. Similar claims by the administration about noncitizens registered to vote in other states crumbled under scrutiny.

In an Oct. 20 lawsuit*, Democrats seeking to block the Trump administration from threatening the integrity of the midterms cite several examples of state and local election officials who have asked for further information when presented with lists of alleged noncitizens only to be rebuffed.

In July, DHS alleged that thousands of potential noncitizens were registered in Pennsylvania, New Jersey and Nevada, but those claims fell apart. In Nevada, the Trump administration claimed to have identified 15,903 noncitizens on its voter rolls. That number was later revised to 185, all of whom were determined to be lawful citizens after further review.

Pennsylvania Secretary of the Commonwealth Al Schmidt (R) met with DHS officials on Aug. 13 to discuss the list his office received “where DHS representatives ‘explained that they did not have high confidence’ that the
14,576 registrants were in fact noncitizens,” according to the Democrats’ lawsuit.

DHS first contacted California about a purported 190,800 noncitizens allegedly registered to vote in the state in a July 16 letter that did not disclose any methodology for identifying those names. 

In a July 23 response, Secretary of State Shirley Weber (D) asked for more details on how DHS compiled its list. The Trump administration didn’t respond until it sent another letter to California on Oct. 14 – after voting had already begun – now claiming 20,000 noncitizens were registered to vote and threatening to sue the state if it didn’t remove those names within 48 hours.

In their lawsuit, the Democrats said this is all part of the Trump administration pattern of  “peddling spurious and ever-changing lists of noncitizens purportedly on state voter rolls, while browbeating States with demands to remove those voters.”

*The Elias Law Group (ELG) represents the Democrats in this case. ELG Firm Chair Marc Elias is the founder of Democracy Docket.