Homeland Security Secretary Markwayne Mullin warned on the 25th anniversary of 9/11 that another terrorist attack remains a question of “when,” while arguing that sanctuary jurisdictions make it harder for federal authorities to protect the country.
Homeland Security Secretary Markwayne Mullin warned Friday that the United States remains vulnerable to another terrorist attack, using a 9/11 anniversary address to argue that sanctuary city policies create dangerous gaps in federal law enforcement.
Speaking at the Department of Homeland Security’s Resilience Plaza in Washington, Mullin credited the department with helping prevent another attack on the scale of Sept. 11, 2001. However, he cautioned that the evolving threat from foreign terrorist groups, domestic extremists, drones, and other emerging tactics makes another attempt a “matter of when.”
Mullin did not identify a specific, imminent plot. His warning came as federal authorities circulated a bulletin saying foreign terrorist organizations continue to encourage attacks in the United States and may use the 25th anniversary of 9/11 to inspire violence or hoax threats.
The bulletin said potential attackers have demonstrated a willingness to act with little or no warning, according to ABC News.
Mullin targets sanctuary jurisdictions
Mullin’s remarks moved from the broader terrorism threat to the administration’s continuing dispute with cities and states that limit cooperation with federal immigration authorities.
“It is tough to sometimes fight, and I’m not trying to get political here, but I will,” Mullin said.
“Sanctuary cities, where they don’t want us to go into, and they’re harboring and abetting activities just like this. They can say it’s for humanitarian purposes, but the truth is, when you become a sanctuary city and you were not supporting law enforcement and you are not allowing law enforcement to do their job, it is a safe haven that incubates terrorist activity.”
Mullin named Seattle, San Francisco, New York City, Boston, and Fairfax, Virginia, as jurisdictions where local restrictions can impede federal enforcement.
“And it does not just stay local in Seattle or San Francisco or New York City or Boston, or even Fairfax, Virginia,” he said. “It bleeds into other parts of the country.”
Sanctuary policies generally restrict when local police or jail officials may share information with Immigration and Customs Enforcement or hold someone beyond a scheduled release based solely on an ICE request. They do not prevent federal agents from enforcing federal immigration law inside those jurisdictions.
Supporters argue the restrictions encourage immigrants to report crimes and cooperate with local police without fearing deportation. The Trump administration contends that the policies allow removable immigrants, including some with violent criminal histories or suspected terrorist connections, to remain in American communities.
Federal bulletin describes changing danger
The security bulletin issued before the anniversary did not specifically attribute the terrorism threat to sanctuary jurisdictions. It warned that overseas terrorist organizations continue to promote attacks and that conflicts in the Middle East could intensify grievances against the United States.
DHS described the country as facing a “heightened and increasingly complex terrorism threat environment.”
“Before 9/11, the primary concern came from centralized international terrorist organizations. Today, those groups remain a threat, but the landscape is broader and more dispersed,” a DHS spokesperson said. “Individuals and small cells now plot attacks independently, often motivated by a range of ideological and political goals.”
ISIS and al Qaeda continue to seek opportunities to conduct or inspire attacks inside the United States, the department said. Domestic terrorists motivated by anti-government beliefs and other causes also remain a concern.
Federal officials said the FBI had arrested at least 16 people during the previous 18 months for allegedly plotting or supporting attacks on behalf of ISIS or al Qaeda.
The Office of the Director of National Intelligence’s 2026 threat assessment estimated that ISIS had as many as 18,000 members worldwide, while al-Qaeda’s broader network included up to 28,000. The groups increasingly rely on digital propaganda to inspire supporters in Western countries where organizing large, centrally directed operations is more difficult.
Drones and artificial intelligence add new concerns
DHS also warned that extremists are experimenting with generative artificial intelligence to produce propaganda and research explosives or biological agents.
“Terrorists are increasingly experimenting with generative AI, not only to create and circulate violent online propaganda, but to explore ways to use explosives and biological agents to conduct attacks,” the department said.
Federal authorities are separately preparing for the possibility that terrorists could use commercially available drones to strike critical infrastructure or interfere with emergency personnel. The United States has not experienced a large-scale terrorist attack involving drones, but the technology has become a central concern for the FBI and DHS.
The immediate anniversary warning did not describe a known plan involving drones, biological weapons, or AI. It instead outlined capabilities that terrorist groups may attempt to exploit.
Debate over federal pressure continues
Mullin has previously proposed withholding federal money from sanctuary jurisdictions and reconsidering federal customs operations at international airports serving cities that resist the administration’s immigration policies.
He said earlier in September that administration officials were examining how federal funding could legally be withheld. Any broad effort to condition grants or withdraw personnel would likely face court challenges and strong opposition from state and local officials.
The administration has also cited recent immigration operations as evidence that federal intervention is needed. During “Operation Rotten Apple,” ICE arrested more than 2,100 people in New York, including individuals with convictions or allegations involving murder, sexual offenses, kidnapping, and drug trafficking, according to a DHS account of the operation.
Mullin’s address connected that immigration dispute to the department’s founding mission after 9/11. His warning did not establish that another attack is imminent, but it underscored the administration’s view that fragmented cooperation between federal and local authorities could leave vulnerabilities as terrorist tactics become more decentralized and difficult to detect.
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