FBI Director Christopher Wray is making his first extensive remarks about the Jan. 6 riot at the U.S. Capitol before a Senate panel Tuesday, as the agency grapples with how to combat violent domestic extremism in the wake of the attack.

Around 300 people have been charged with federal crimes in connection to the attack, ranging from trespassing to conspiracy and assault charges, laying bare the bureau’s challenges in stopping politically motivated violence before it occurs.

The hearing before the Senate Judiciary Committee comes as the Federal Bureau of Investigation is confronting criticism for not pre-empting the violence, with lawmakers from both parties suggesting it should have acted more forcefully, given the warning signs. On Jan. 5, the FBI’s Norfolk, Va., office warned in a report that online message-board traffic urged people to go to Washington “ready for war” and shared maps of the Capitol, law-enforcement officials have said. However, the information in the report was uncorroborated and investigators were unable to link it to specific people, making follow-up difficult.

Mr. Wray is facing questions both about why law enforcement hadn’t anticipated the extent of the violence and how the bureau is planning to tackle future acts of extremism.

A senior FBI official told reporters Friday that domestic violent extremists have caused more deaths in the U.S. than overseas terrorists in recent years, with evolving motives. In 2019, the official said, the bureau viewed racially-motivated extremism as the most potent domestic terror threat but has shifted to view antigovernment extremism as the top threat in 2020 and the current year.