Since Markwayne Mullin became secretary of the Department of Homeland Security in March 2026, the agency has taken a much more prominent role in President Donald Trump’s campaign to strengthen election security and investigate what the administration describes as vulnerabilities in the nation’s voting system.

Mullin, a former Republican senator from Oklahoma and longtime Trump ally, was sworn in as DHS secretary on March 24, replacing Kristi Noem.

His appointment placed him at the head of one of the federal government’s largest agencies, with responsibilities ranging from border security and immigration enforcement to cybersecurity, disaster response and counterterrorism. But elections have increasingly become part of that portfolio.

The development is significant because elections in the United States are primarily administered by states and local governments. Federal officials have traditionally played important supporting roles, particularly in cybersecurity and protection against foreign interference, but direct federal involvement in voter-list administration has long been politically sensitive.

Under Mullin, DHS has moved more aggressively into that debate. The administration argues that stronger federal involvement is necessary to ensure that only eligible citizens participate in federal elections.

Critics counter that the administration is expanding federal authority into an area traditionally controlled by states while relying on data that may contain errors. At the center of the controversy is the administration’s effort to identify potential noncitizens on state voter-registration lists.

In July, Mullin announced that DHS had identified large numbers of people it said might be noncitizens appearing on voter rolls in several states. The administration subsequently cited a combined figure of roughly 250,000 potential noncitizens across California, Pennsylvania, New Jersey and Nevada. The wording is important.

Being identified as a potential noncitizen on a voter list does not necessarily mean that the individual illegally voted. A person can appear on a voter-registration database because of outdated records, mismatched information, database errors or problems with how government systems compare records.

That distinction has become one of the central arguments surrounding the administration’s claims. State election officials have challenged some of DHS’s findings and requested more information about how the department reached its conclusions.

Officials in Nevada and California, for example, have questioned the methodology and reliability of the data used by the federal government. The controversy goes beyond statistics. It raises a fundamental question about the relationship between Washington and the states: How much authority should the federal government have over election administration?

Trump has made election integrity a major political issue throughout his career, particularly since the 2020 presidential election. He has repeatedly argued that the American election system contains serious vulnerabilities, while numerous election officials and courts have rejected claims that widespread fraud changed the outcome of the 2020 election.