He waved a gun in her face and grabbed her by the hair, slammed her to the ground, and dug his knee deep into her back. She was still in her bathing suit - the fourteen year old had just left a pool party. The officer was white, the teenager was black.

It happened this weekend, in McKinney, Texas, and once again we only know about it because somebody with quick instincts taped the violent confrontation between police and a group of teens, and released it to the media. The officer has now been disciplined, thanks to the video. But he still has his job -- and we've all been given another front row seat to the crisis in policing that's pushing our country's social fabric to the breaking point.

In the last months as Ferguson and Baltimore blazed, Congress has sat on its hands. But finally momentum is stirring -- with a new Senate bill to track police use of force nationwide, co-sponsored by Barbara Boxer. Lawmakers who want to do right will only step up if they think we have their back, so sign and get the word out now. This could be a huge moment: