Investigators may have broken state laws under the direction of top Homeland Security leaders as part of an expansive effort to find noncitizens on the nation’s voter rolls, according to a federal whistle-blower’s account released on Monday. The authorities also required agents to examine at least 40 voters each day, suggesting a rushed pace that raises questions about the thoroughness of the investigation. The effort has relied on questionable data and has likely improperly flagged U.S. citizens who are eligible to vote, the whistle-blower said in a nearly 30-page report.

The whistle-blower report, provided to Senators Chuck Schumer and Alex Padilla, both Democrats, offers an inside view of what the Department of Homeland Security is calling the “Unlawful Voter Initiative.” The New York Times revealed last month the existence of the operation, which has deployed hundreds of federal agents to scour voter rolls managed by the states in a widespread hunt for evidence of voter fraud. The investigation stems from President Trump’s longstanding fixation on noncitizen voting, despite decades of research showing the practice is vanishingly rare.

Democrats and voting rights activists have denounced the operation as another way Mr. Trump is trying to sow doubts about the legitimacy of U.S. elections. They fear that eligible voters could be disqualified from participating in the fall midterms, or worse, that Mr. Trump will use the investigation to try to discard actual results. “This is just the latest example of how far Donald Trump will go to interfere in our elections,” Mr. Schumer said. On Sunday, the senators sent a letter to Markwayne Mullin, the Homeland Security secretary, demanding that the operation be halted and seeking answers to a dozen specific questions. The senators included the full whistle-blower account, produced by Democracy Defenders Fund, a nonprofit watchdog group founded in 2023.

In a statement, the Department of Homeland Security broadly defended its hunt for election fraud: “Our message to aliens who vote in American elections is clear: we will find you, arrest you, and you will face the consequences — including criminal charges and deportation.” The identity of the whistle-blower is not known to The Times. Democracy Defenders Fund said the whistle-blower requested anonymity because of “an extreme fear of retaliation but they feel an obligation to speak up about the misconduct and gross mismanagement they have witnessed.” According to the whistle-blower, agents are expected to complete at least 40 reviews in each eight-hour day, giving them about 12 minutes to determine each voter’s citizenship and voting history. The consequence of the investigation is potentially vast, because each review is recorded in a database that could affect individuals’ immigration status or legal permanent residency.