President Biden is reviewing the U.S. government's response to domestic extremism, including threats that gained traction under President Donald Trump.

The assessment begins as the Department of Homeland Security issued a public warning of possible attacks on government facilities or officials. The advisory referenced the Jan. 6 attack on democracy at the U.S. Capitol and other incidents going back years, such as the 2019 mass murder in El Paso, Texas, blamed on a man who had written an anti-immigrant screed. The advisory says extremists are motivated by election conspiracy theories as well as pandemic conspiracy theories.

The Trump administration was often accused of downplaying the danger of white supremacists and other extremists — but the DHS bulletin shows that security officials within the government now feel free to express their concerns.

"My sense of that alert is that it was probably a long time coming," says Chris Krebs, who was a top DHS official appointed by Trump and then fired by Trump for accurately saying that last year's election was secure.

Biden administration officials did not elaborate on what they called "information" pointing to possible future attacks, so NPR took its own snapshot of the current threat.

The state of domestic extremism is unusually visible at the moment because it was on display at the Capitol on Jan. 6. NPR's Hannah Allam, who has covered domestic extremism for years, witnessed the attack. "Standing outside the Capitol that day, I saw all the strands of American extremism in one place," she said. "All the groups that I cover under one umbrella there. The established groups were there, the white nationalists, the neo-Nazis, some of the militia groups."

"But the most disturbing part," she said, "is that now, side by side with organized violent actors, you have thousands of otherwise ordinary conservatives who are fans of Donald Trump." Believing the former president's lies about his election defeat — known as the "big lie" — as well as the QAnon conspiracy theory and other falsehoods, they mingled with extremist groups in what analysts view as "mass radicalization."

Robert Pape, a specialist in political violence at the University of Chicago, analyzed the backgrounds and statements of some of the known Jan. 6 Capitol rioters. He and a team gathered information about 193 of the people who were arrested after the insurrection at the Capitol.

Their analysis found that some Capitol attackers are linked with right-wing extremist groups like the Proud Boys or the Oath Keepers. But most are not. Many are older people, with good jobs.

"Twenty-seven percent are white collar — that is, doctors, attorneys, architects. This is so unusual that in our past studies of the demographics of political violence, we don't even have categories for business owner and white collar," Pape said.

This wide range, from states across the U.S., suggests how deeply election falsehoods penetrated mainstream society. Many attackers said they felt Trump told them to act. The former president's incitement of the attack is now the subject of his Senate impeachment trial next week.

"The bottom line is that we are on the beginnings of a problem that's likely to be with us not just for months, but for years," Pape said. "The sharpest rise of political violence in the world is happening in the United States."

Pape has studied political violence around the world for decades and in the past year found it was essential to turn his focus on his own country. He now sees a pattern he has perceived elsewhere.

"We have all the ingredients to unfortunately see the possible acceleration of the growth of this movement. We see that there is a leader with demonstrated support for extralegal activity. We see mass grievances perceived by large masses of people. We also now see a deadly focal point event," Pape said.

The U.S., of course, has its own history of violent political movements, such as the rise of the Ku Klux Klan after the Civil War, in an earlier era of racial and demographic change. The U.S. also has its own specific problems with disinformation.

Krebs, who now studies disinformation for the Aspen Institute, said the best way to ease the flood of it would be for those who supported the "big lie" to take responsibility and own what they did. This is unlikely, so Krebs looks to Plan B: "You have to hold them accountable through other means." Trump faces a Senate impeachment trial next week for inciting the Capitol attack.

The Biden administration's review of the U.S. government's capacity to fight domestic extremism is likely to find less robust capabilities than it has for international terrorism.

"The international infrastructure really dwarfs what the U.S. government has for domestic terrorism. Domestic terrorism has always been a little bit of a backwater," says Michael Leiter, a former head of the National Counterterrorism Center, which by law focuses on international threats.

The legal and political barriers to enforcement can also be greater because the U.S. government is obliged to respect the rights of U.S. citizens. What do you do, Leiter says, if you're an FBI agent and learn of a citizen who's armed and speaking harshly about the government? Americans have a rightto be armed and speak harshly about the government.

Distinguishing radicals from law-abiding citizens was not easy after the Sept. 11 terrorist attacks, when Muslims became special targets of attention. Leiter himself acknowledged that "I and others made many mistakes and undoubtedly unfairly profiled some individuals based on their religion — not purposefully, but the system did that."

Counterterrorism officials will need to avoid profiling right-wing figures — both because the Constitution requires it and because they will likely have defenders in Congress.

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