Islamist terrorists are busier than ever trying to kill us. That’s a fact.

Two years ago, The Heritage Foundation conducted an exhaustive review of publicly available U.S. court and federal and state government records. The researchers documented at least 60 terrorist plots related to Islamist extremism following the 9/11 attacks—all aimed at the U.S. And the pace of plotting has only quickened.

There have been nine additional plots since that report came out in 2013. Seven occurred this calendar year, six since April. Plot number 69 was thwarted just a few days ago. On June 2, federal law enforcement officers killed Usaamah Abdullah in Boston. Dawud Sharif Abdul Khaliq, an alleged accomplice, was arrested later. It is suspected they intended to behead anti-Islamist activist Pamela Geller.

So, yes, Islamist terrorism in America is on the rise. The numbers don’t lie. Still, there is a ferocious debate over what they mean.

No one has paid more attention to terrorist trends in the United States than Cato Institute senior fellow John Mueller. In 2011, he co-authored “Terror, Security and Money: Balancing the Risks, Benefits and Costs of Homeland Security” for Oxford University Press. Mueller conducted an exhaustive study of terrorism threats in relation to other risks faced by everyday Americans. He concluded Washington obsessions with combating terrorism were overblown. Other dangers killed and maimed many more citizens than terrorists.

“The rise of terrorism is a hazard to human life,” Mueller wrote in an updated 2014 risk assessment, “and it should be dealt with in a manner similar to that applied to other hazards—albeit with an appreciation for the fact that terrorism often evokes extraordinary fear and anxiety.” Since other risks are greater he argues, counterterrorism efforts ought to be scaled back.

Mueller’s latest study was published right before ISIS started to make headlines gobbling up territory in Syria and Iraq and beating the drum for more attacks on the U.S. homeland. Still, Mueller would be unimpressed. After all, of the 69 post-9/11 plots, only five came to fruition. (The most recent of these came last year, when Zale Thompson attacked and injured two New York City police officers with an axe.) And, all together, they resulted in a very limited loss of life. These numbers seem to reinforce Meuller’s conclusions.

If Mueller provided the right context for evaluating the domestic terrorist threat he might be right. But he is wrong. According to Mueller, the distinguishing feature of terrorism is that it sparks obsessive fear. On that score there is social science research to back him up. People-generated disasters (such as terrorist attacks and riots) evoke more anxiety and apprehension than acts of nature.

But, “fear” is not what uniquely distinguishes terrorism as a human hazard. Terrorism is an act of “political” violence. Terrorists are not just trying to kill people and destroy property. They are trying to undermine the political order and civil society. Thus, they represent a fundamental threat to the system that provides security, protects liberty and promotes prosperity. Terrorism is a danger to all members of the community, not just the specific victims. As a public policy problem, it does represent an outsize concern beyond just counting the number killed.

Getting beyond the body count, there are a number of reasons to be concerned about the recent up-tick.

Plots are increasingly homegrown. That means they are hatched here by individuals who are self-radicalized and operating without formal ties or instructions to overseas terrorist organizations. Finding and upending these threats requires scrupulous, persistent and effective domestic intelligence and law enforcement operations.

While the terrorists are here, however, their inspiration is abroad. Increasingly, radicalized individuals are found to be inspired or in dialogue with extremists entities overseas. ISIS successes in the field, its sophisticated social network activities and its ability to recruit fighters globally are all real cause for concern.

What the U.S. faces now is a transnational terrorist threat more complex than the enemy that confronted America on 9/11. Terrorists are linking social networks and human webs, and that creates unprecedented opportunities to operationalize violence.

Defeating this threat will require both continuing to disrupt plots here at home and defeating the overseas terrorists who inspire them. That will require an expenditure of resources far outsized to the formula suggested by Mueller’s risk assessment.

Originally published in Forbes