“It’s like, every time we come together for something like this, there is someone new we are introduced to for the first time, and we know the road that’s ahead of them,” said Ms. Smegielski over a basket of chicken nuggets. A tattoo honoring her mother is on her right arm.

She looked at Mr. Goddard, to her right; both work for Everytown for Gun Safety, an advocacy organization backed by Michael R. Bloomberg, the former New York mayor. “Just like you were there for me three years ago,” she told him. “And now, I’m somebody’s Colin.”

Mrs. Maisch had cut short a family reunion in St. Louis to be here for the vote. In 2013, when the Senate voted against gun safety measures that President Obama pushed for after the Sandy Hook shooting, she stood up in the Senate gallery, looked down at the lawmakers and shouted, “Shame on you!” She was escorted out by the police and detained for two hours.

On Monday, she wore an orange button that read “Survivor” and a collection of colored plastic wristbands, each one representing a shooting victim. One was for a congressional candidate from Wisconsin whose mother killed herself. One was for Jordan Davis, a 17-year-old student shot in Florida, by someone who complained about his loud music. One was for Dawn Hochsprung, Ms. Smegielski’s mother.