It’s September 11th. We’re sharing and remembering the events of that day, and as I do every year I remember where I was: a freshman in high school, watching the World Trade Center ablaze during my second period history class. But how do you commemorate September 11th if you don’t remember it—because you were too young, or because you’ve become ideologically warped? Daniel Byman writes:

Today’s students … lack a sense of historical perspective. In the late 1960s and early 1970s, there was an average of more than one airplane hijacking per week globally, and those two decades saw hundreds of bombings in the United States by groups ranging from the Ku Klux Klan to the Weather Underground. Indeed, on U.S. soil, both terrorist incidents and fatalities are down in the post-9/11 era compared with the years before.

However, because 9/11 defines what a terrorist incident can do, a bombing or shooting, especially if done by a Muslim in the name of jihad, looms far larger in the imagination than it did in the past. It is hard for students to picture a country remaining relatively calm about a 1970s-level pace of attacks. It is also difficult for them to imagine a U.S. government with only dozens, not tens of thousands, of counterterrorism officers.

Although most students would be loath to admit it, based on class discussions they often seem to agree with Trump on some of his assumptions about how to respond to the terrorism threat. They are skeptical of intervention in the Middle East, especially on a massive scale. However, they also accept a grinding set of miniature wars, with air strikes and special-operations force deployments in much of the Muslim world on a near constant basis. They are also comfortable working with dictatorships in the Middle East, seeing this as a necessary price for counterterrorism cooperation. Perhaps most important, they often see every emergence of a jihadi group as a potential threat to the United States, and thus Islamic State-linked attacks in the Democratic Republic of the Congo and Sri Lanka are seen as proof of a continued danger to the United States.

The events of 9/11 are increasingly a memory, and without education that memory can easily become a caricature. Americans who are not fortunate enough to study at an elite university are particularly susceptible to vague threats being used to justify unnecessary government spending or an administration’s preferred policy, without a recognition of how the dangers facing the country have changed since 2001. Capturing all the nuances surrounding 9/11 is vital, but the proper response today also requires recognizing that terrorism is constantly evolving, and when it strikes again it may not come from an expected or familiar source.