DHS Secretary John Kelly: 'We are a nation under attack' Kelly laid out his strategic vision for the department Tuesday.

 -- Secretary of Homeland Security John Kelly offered an unapologetic view of his department and the Trump administration's goals for the nation's safety, telling a Washington, D.C., audience that "we are a nation under attack."

On Tuesday, Kelly said the United States is under attack from all kinds of bad actors -- criminals, homegrown terrorists, cyber-terrorists, smugglers, transnational criminal organizations, failed states, "sadistic radicals" and "people who hate us," among others.

The comments came during a speech at George Washington University in which Kelly shared his strategic vision for the Department of Homeland Security (DHS). The retired Marine Corps general laid out his top concerns, ranging from transnational criminal organizations to homegrown terrorism, drugs and cyber attacks.

Kelly devoted the majority of his remarks to the "relentless" threat of criminals and potential terrorists crossing into the U.S. over the southern border and made particular note of the crime that is fueled by Americans' appetite for drugs. On that point, Kelly said that DHS would enforce existing marijuana laws.

"Let me be clear, it is a potentially dangerous gateway drug," said Kelly, pointing out that the use and possession of marijuana continue to be "against federal law," even as several states have taken steps to decriminalize it.

"When people think about DHS, they think about how we respond to terrorism. This is our foundation, given our origin story, and a critical part of what we do," said Kelly. "But our jobs are to secure the nation from the many other threats we face -- from all hazards."

Kelly said that like terrorists, "transnational criminals inflict unthinkable brutality, and regularly behead their victims."

"They take the form of drug cartels, or international gangs like MS-13, who share their business dealings and violent practices. Their sophisticated networks move anything and everything across our borders, including human beings," he said.

He repeatedly raised concerns about foreign fighters in places like Iraq and Syria that are returning home to "visa waiver" countries in Europe.

"They want to get here and do us harm," he added.

He also stressed the cyber threats that the U.S. currently faces.

The threat is "more than bombs and guns," he said. "We are under constant attack by a wide range of adversaries with an even wider range of capabilities" from state actors to lone wolves, said Kelly.

ABC News' Adam Kelsey contributed to this story.