Who were the Trump supporters that stormed the US Capitol, how did they pull it off?

Hundreds of Trump supporters stormed the Capitol building on Wednesday, ransacking the House and Senate chambers and the offices of some lawmakers. Four people died and more than 50 Capitol and DC Metro police officers were injured. DC Mayor Muriel Bowser called the Capitol Police’s response a failure.

About 70 people have been arrested so far. The Justice Department is pledging to criminally charge more of the rioters, and the FBI asked the public for help identifying them. The big question: How was the violence able to get so out of hand?