This happened in Minnesota. From the Star Tribune:

Authorities partly closed a downtown Minneapolis freeway briefly Tuesday morning as they made a “high-risk” traffic stop to detain a motorist who allegedly brandished a gun at another driver.

Turns out the driver was an agent for the Bureau of Alcohol, Tobacco and Firearms, a State Patrol report said.

[ . . . ]

The State Patrol took the man into custody but released him after officers learned he was an ATF agent who was carrying proper credentials.

“It’s under investigation,” said Lt. Eric Roeske of the Minnesota State Patrol. “We’re trying to determine the facts of what occurred.”

License to brandish. License to kill. Your government at work.