For the two decades after the Sept. 11, 2001, attacks, such exercises and drills often focused on the possibility of an internationally inspired terrorist attack. But the scenarios practiced by the Biden administration last year, one of which involved roughly 80 agencies, envisioned scenarios far closer to what happened on Jan. 6.

In a May exercise, a protest on the National Mall became violent and worsened when social media drew more people into the sprawling, fast-moving conflict. The September scenario involved simulated protests around the steps of the Supreme Court, followed by clashes that spread through the area, crossing the jurisdictional lines of various law enforcement agencies.

The first exercise was a tabletop simulation held at Joint Base Myer-Henderson Hall, a military base in Virginia, hosted by the Defense Department. It included the threat of a homemade bomb — another echo of Jan. 6. On that day, an unidentified person planted pipe bombs outside the national Democratic and Republican party headquarters. FBI investigators are still trying to identify and arrest the would-be bomber.

The second effort, conducted this fall in McLean, Va., was a virtual reality exercise stretched out over a week in which clashes outside the Supreme Court spread to other jurisdictions, requiring different agencies to communicate quickly and respond effectively to stem the violence, officials said.

The second senior official said the Biden administration drew a number of lessons from the simulations: among them that agencies need to improve their communications technology to deal with rapidly changing events, and that it is crucial to have a unified command structure to manage law enforcement responses to major incidents.