That does not make sense in a country where we have seen a constant stream of such terrorist attacks to advance wide-ranging political agendas. While 34 states and the District of Columbia have their own antiterrorism laws, many have the same pitfalls as federal law.

Even before Sept. 11, the federal government realized that crimes motivated by terrorism needed to have specific laws with severe penalties. Amid a rising tide of attacks leaving scores dead, why do our current laws give more consistently severe penalties to those plotting on behalf of foreign organizations than to those who want to kill their fellow Americans over American issues? As an example, Conor Climo, a white supremacist arrested last month in Las Vegas for plotting to attack a synagogue and a gay bar with firearms and explosives, faces 10 years for his plot, while in 2018 Alexander Ciccolo was sentenced for twice as long in a plot involving similar tactics because he was acting in support of a foreign group.

The legal line between foreign and domestic terrorists is not just blurry but also misleading. First, it overlooks the fact that a majority of individuals who carried out attacks within the United States for what we consider foreign terrorist groups like ISIS and Al Qaeda have been Americans. For example, Omar Mateen, who killed 49 people at Orlando’s Pulse gay nightclub in 2016 was born in Queens and grew up in Florida. To not consider him a domestic terrorist in the most intuitive sense of the term risks perpetuating the notion that as a Muslim, he was somehow not one of our own. Second, it doesn’t acknowledge the fact that ideologies lumped in the domestic bucket can also be rooted abroad (see Nazism). Given what we have learned about Russian trolling and covert online influence campaigns, we may also underestimate the foreign influence stirring hate on the internet that can incite violence.

We’ve learned in the New York Police Department that extremists of all varieties are also acting increasingly alike. As examples, ISIS and the lethal neo-Nazi group the Atomwaffen Division have both learned that pushing internet propaganda telling their audiences whom to hate, why to hate them and how to kill them is an effective mobilization tool. They have both relied on anonymized or encrypted social media channels, chat applications and gaming platforms to avoid law enforcement while getting their messages out. They have both encouraged relatively unsophisticated but deadly tactics that can be deployed with little planning and money, making such attacks doable for a wider pool of followers.

Make no mistake, they have learned from each other: James Alex Fields’s vehicle attack at the Unite the Right rally in Charlottesville, Va., in 2017 that killed Heather Heyer and injured 28 others was a page out of the ISIS playbook. Mr. Fields was charged with a hate crime, but not as a terrorist.