At Monday’s congressional hearing on the Secret Service and the assassination attempt against former President Donald Trump, Rep. Raja Krishnamoorthi asked: “What can Congress actually do to stop this from happening again?”

The congressman, a Democrat from Illinois, then showed the chamber a graphic on political violence that was published a month ago by the Chicago Project on Security and Threats, which I lead. The graphic shows that 74% of Americans want members of Congress to come together to denounce all political violence. This stance crosses party lines, with 86% of Democrats, 51% of independents and 70% of Republicans saying so.

(Chicago Project on Security & Threats)

While individual members of Congress have made statements denouncing the Trump assassination attempt, Krishnamoorthi challenged the entire House of Representatives to go much further, proposing a resolution in the near future “condemning any political violence in America” and calling for support from every member of the chamber. Such resolutions go to the House for a vote and are not signed into law, but they convey a message — especially when they pass unanimously.

After Monday’s grueling hearing, the head of the Secret Service resigned on Tuesday, writing to her staff: “I take full responsibility for the security lapse.” That departure will not prevent future bloodshed. However, Congress has a chance to do so.

At this critical time, members of Congress — both Republicans and Democrats — must stand together to oppose political violence. The Trump shooting is only the latest of a growing string of incidents. Indeed, we are seeing the most violent era in American politics in decades, and now is certainly the time for all political leaders at all levels of government — national, state and local — to adopt similar resolutions and make similar unified statements.

Political violence in the United States is entering a new stage as America faces mounting domestic terrorism: violent anti-government and other political actions by militias, small groups and volatile individuals within the United States.

To be sure, famous acts of domestic terrorism occurred from the 1990s through 2010, including the violent standoff at Ruby Ridge in 1992, the Oklahoma City bombing in 1995, the violent protests against the World Trade Organization meeting in Seattle in 1999, and the multiple arsons and bombings conducted by individuals affiliated with the Earth Liberation Front and Animal Liberation Front from 1995 to 2010.

What’s happening now is different. Political violence in America is escalating, both in number and in kinds of violent incidents. Since even before the pandemic, America has witnessed an era of political violence unparalleled at least since the 1960s. Incidents of domestic terrorism increased by 357% between 2013 and 2021, according to statistics collected by the FBI and the Department of Homeland Security.

Collective political violence is rising too. Since summer 2020, the United States has seen major political riots against police and downtown businesses during some of the George Floyd protests; a brazen assault on the U.S. Capitol to stop the peaceful transfer of power on Jan. 6, 2021; spikes of campus unrest to protest the conflict in Gaza in fall 2023 and spring 2024; and numerous lone wolf attacks and plots — including against the husband of then-Speaker Nancy Pelosi, against Justice Brett Kavanaugh and against Michigan Gov. Gretchen Whitmer.

To better understand this new era, the Project on Security and Threats has set up more than a dozen national surveys in the three years since Jan. 6, 2021. These rely on high-quality nationally representative samples that match the American adult population on a vast number of demographic, political, economic, social and other factors, meaning it is reasonable to extrapolate the findings to the U.S. population as a whole.

The striking finding from our June 24 survey is that 10% of American adults — the equivalent of 26 million people — agreed that “the use of force is justified to prevent Donald Trump from being president.” The poll also found that 7% of American adults — the equivalent of 18 million people — support the use of force to restore Trump to the presidency.

The assassination attempt against Trump less than three weeks later did not come out of nowhere. The shooter’s motive is not yet clear — he seems to have researched President Biden as a target as well — but in any case, we need to be concerned about copycat and retaliatory violence by volatile individuals steeped in incendiary political rhetoric, beset by mental illness or simply looking to gain notoriety. Such spirals of violence could occur against many political leaders and at numerous flashpoints in the months ahead during and after the presidential election.

No one can entirely prevent that, but for lawmakers, the next step is clear: Accept Krishnamoorthi’s challenge and pass a resolution, unanimously, condemning political violence. This could make a major difference.

Just as studies show that incendiary political rhetoric encourages support for political violence, so too would public condemnation reduce it. Those taking violent political action are often volatile individuals, with their own reasons to act out, but also encouraged by the perceptions that they are serving some greater good. Some hope to be glorified as warriors for a cause. Leaders of those causes should make clear that no one who engages in political violence will be glorified.

The most effective message to reduce support for violence is a simple one: Political violence, wherever it comes from, is illegal, immoral and anti-American. Leaders should also contribute to a culture of prevention by encouraging political anger to be redirected away from negative expression as violence and toward positive expression as voting.

Since the assassination attempt, Biden has already given multiple speeches along just these lines. I hope that his courage will be contagious and that Congress will do its part. It is possible to reverse the rising violence and return to the peaceful traditions that made American democracy the envy of the world.

Robert A. Pape, a professor of political science at the University of Chicago, is the director of the Chicago Project on Security and Threats.