What’s the graver threat to homeland security today: Domestic or international terrorism?

It’s been 20 years since al-Qa’ida terrorists hijacked commercial airliners and flew them into buildings and fields on Sept. 11, 2001, killing 2,977 Americans in the process.

While American military forces have pursued and killed terrorists and their harborers across the Middle East and South Asia, security experts have warned that groups like al-Qa’ida and ISIS still represent major threats that could strengthen in the wake of the U.S. withdrawal from Afghanistan.

What’s more, homegrown terrorists have started to pose a less predictable but more frequent threat to homeland security. The FBI cites the Jan. 6 Capitol riots, the attempted kidnapping of Michigan Gov. Gretchen Witmer and the Portland riots as examples of domestic terrorism.

“The public’s understanding of the word ‘terrorism’ is equated to these massive destructive acts of mass violence that kills hundreds or thousands of people.” national security consultant Daryl Johnson said. “But really, terrorism can take all kinds of forms. It doesn’t really need to have a fatality.”

A majority of domestic terror can be traced back to domestic extremists, like neo-Nazis and militia movements, turning violent. A Center for Strategic and International Studies report found that acts of far-right terrorism significantly outpaced other forms of terrorism over the last 25 years.