Capitol Police chief resigns amid pressure after mob breach

• Capitol Police, who are charged with protecting Congress, were overwhelmed by rioters who stormed the Capitol building and made their way into the Senate chamber, as well as some lawmakers' offices.
• Rioters remained in the building for hours, until members of the National Guard and other law enforcement agencies arrived to help Capitol Police clear the mob.

What they're saying: Gus Papathanasiou, chair of the U.S. Capitol Police Labor Committee, said in an emailed statement earlier Thursday that the breach was "a failure of leadership at the very top."

• Papathanasiou said he was "incredibly proud of the individual officers," but "they lacked the immediate backup and equipment needed to control the surging crowd as events quickly spiraled out of control."
• “We have several protesters dead, multiple officers injured and the symbol of our Democracy, the U.S. Capitol, desecrated. This never should have happened.”

• The union called for "leadership change at the highest level" including Sund and his senior command staff.

Earlier Thursday, Sund said the force is "conducting a thorough review of this incident, security planning, and policies and procedures."

What to watch: Several lawmakers have vowed to investigate law enforcement's response to Wednesday's violent U.S. Capitol breach.

Go deeper: Biden, activists decry "double standard" in police response to mob at U.S. Capitol