In the famous black-and-white film clips, Chicago police wade into crowds at the 1968 Democratic National Convention with billy clubs flying.
These days, officers know that kind of confrontation will quickly land on YouTube. And they've adopted softer crowd-control tactics.
But the many thousands of protesters expected for next week's summit of NATO leaders could pose the department's greatest challenge in years.
The summit carries high stakes for a police force that never completely shed its reputation for brutality. It's also a big test for Police Superintendent Garry McCarthy, who leads the 12,000-member force.
McCarthy says he's committed to extracting troublemakers rather than overwhelming entire crowds. And he wants to change the way police view demonstrators.