Richard B. Zabel oversaw terrorism prosecutions as deputy U.S. attorney in the Southern District of New York from 2011 to 2015 and teaches national security law at Columbia Law School.

The United States faces a rising threat of violent extremism yet has no law targeting the problem. The Jan. 6 attack on the Capitol and the Department of Homeland Security’s first-ever national domestic terrorism bulletin on Jan. 27 have sounded the alarm that it is time for Congress to fix this gap: We need anti-terrorism laws aimed at domestic terrorism.

The Patriot Act, passed in the aftermath of 9/11, defined domestic terrorism as criminal acts in the United States that are “dangerous to human life” and appear “intended to intimidate or coerce a civilian population or to influence the policy of a government by intimidation or coercion” or “to affect the conduct of a government by mass destruction, assassination or kidnapping.” The definition clearly fits the Jan. 6 insurrection and other violent extremist incidents, but it is largely useless for charging individuals as domestic terrorists.

Why is this? First, although the law provided officials with additional authority to investigate domestic terrorism, it created no new criminal offense of engaging in domestic terrorism. This means that a prosecutor cannot charge a defendant with domestic terrorism alone. Instead, prosecutors have to use other available statutes, such as firearms or assault statutes. But when terrorism cases are not pursued as terrorism cases in our courts, it limits our societal condemnation of the defendants and their dangerous ideologies. Juries, judges and the public do not get to pass judgment on the conduct as terrorism.

A second problem is that the definition of domestic terrorism is too narrow, even if it were to carry criminal penalties. For example, by requiring such acts to be “dangerous to life,” the definition excludes common tools of terrorism such as criminal threats, non-life-threatening physical assaults, damage to property and other acts intended to intimidate or coerce. These acts were on brazen display on Jan. 6.

On that day, many in the mob used force and made their bloody intent clear, but through dumb luck did not kill or seriously harm anyone. Prosecutors will have difficulty appropriately charging many of these would-be violent terrorists. For example, if a person surged up the Capitol steps, forcing his way past police, and cheered as fellow insurgents beat a police officer, what can he be charged with? What about those who possessed weapons and yelled threats but no more? Calling these crimes merely federal trespassing, disorderly conduct or weapons possession is not enough. Well-defined laws could appropriately address this varied conduct and call it what it is: domestic terrorism.

History supports the need for new laws to address domestic terrorism. During Reconstruction, the country confronted terrorism by the Ku Klux Klan, which opposed the ascent of multiracial democracy. Congress enacted the Ku Klux Klan Act to protect Blacks, Whites and, crucially, the democratic process. Aggressive enforcement of the act effectively destroyed the KKK. Once the law was no longer enforced (and later partly invalidated on questionable states’-rights grounds), the cancers of the KKK and white supremacy returned and metastasized.

Our international terrorism laws offer another example of Congress effectively meeting an emerging terrorist threat. After a truck packed with explosives by Islamist terrorists detonated in the first World Trade Center attack in 1993, Congress took action. It enacted a body of anti-terrorism laws that were innovative and enabled effective prosecution of international terrorists.

But when Timothy McVeigh, an anti-government extremist, detonated a truck bomb in 1995 in Oklahoma City, killing and injuring hundreds and destroying a government building, Congress did not enact equivalent domestic terrorism laws. Nor has it done so during the continuous reign of domestic terror since then. This is a legislative failure.

One legitimate concern in discussing a domestic terrorism law is the threat of overreaching in violation of First Amendment protections. In 1940, with the nation fearful of communism, the Smith Act was enacted to protect the country against the advocacy of force or violence to overthrow or destroy our government. The Smith Act is tainted — rightly — by its overzealous use as a tool of the Red Scare. History calls for caution, but not paralysis. Our courts have made clear that some inflammatory speech is not protected. In Brandenburg v. Ohio, the Supreme Court ruled that if a speaker urges others to use force with words “directed to inciting or producing imminent lawless action,” and likely to do so, that speech is not protected. This strict principle can guide any new domestic terrorism law that looks at speech. Our First Amendment, uniquely in the world, protects almost boundless free speech, including dangerous speech, but it is not a suicide pact.

The historian Richard Hofstadter observed, “American politics has often been an arena for angry minds.” Some of these angry minds engage in angry acts. For too long, domestic terrorism has been ignored by Congress. This lapse culminated in the horrifying Jan. 6 images of a Confederate flag hoisted inside the Capitol and of our elected representatives taking cover on the floor. Congress needs to stand up.

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