When you walk into Sen. Chris Murphy's Senate office, one of the first things you might see is a large poster of children's TV host Mr. Rogers with a quote on it.

"When I was a boy and I would see scary things in the news, my mother would say to me, 'Look for the helpers. You will always find people who are helping,' " Rogers wrote.
The quote was widely shared after the Sandy Hook Elementary School shooting in Newtown, Connecticut, five years ago, where 20 school children and six adults were killed. Below the poster on Murphy's wall is a plaque dedicated to the community of Newtown.
    "I was just outside the room as we told the parents. There are a lot of days when I wish that I hadn't heard the things I heard or seen the things I saw that day. It was a feeling of helplessness that's hard to describe," Murphy said of the shooting. "These parents, they're my age, their kids are my kids' ages."
    On the day of the shooting, December 14, 2012, Murphy waited with parents in a firehouse near the school. Waiting for news that could only be devastating.
    Since that day, and with many of the families of the Newtown victims by his side, Murphy has made it his mission to end what he calls an "epidemic" of gun violence.
    He told CNN it would feel like a "personal failure" if he doesn't make progress on the issue.
    "It wasn't that I didn't have an emotional connection to the issues that I worked on prior to Sandy Hook, but this was different," Murphy told CNN. "This was a calling and a mission in a way that I had never felt before."
    Murphy has pushed for legislative action after mass shootings since Newtown, and has increasingly attacked his colleagues for their inaction.
    Murphy says he is embarrassed he didn't pay more attention to the issue of gun violence before the shooting, the kind that happens daily in American cities across the country.
    "I should have been working on this issue before Sandy Hook because even then every single day 80 people were dying from guns," Murphy said.
    The 2016 election saw Democrats moving to the left on guns, with presidential nominee Hillary Clinton devoting one night of the Democratic National Convention to victims and families of gun violence.
    But even as the issue has given Murphy a platform, progress on his signature issue has been slow since that Friday morning five years ago.
    After the 2016 Pulse nightclub shooting that killed 49 people, Murphy staged a nearly 15-hour filibuster to protest the lack of any serious debate on the Senate floor over possible gun control measures to consider after the tragedy.
    "Like other great social change movements, it will be met with lots of failures before it meets grand success," Murphy said of his efforts. "We don't hear about the social change movements in which people gave up the first time that a bill failed, or an election didn't go their way."
    Murphy says that even though his political career has been defined by a tragedy, his life is richer because of his experience with the families of Newtown.
    "I'm lucky enough that I get to spend time almost every week with these families. I've been able to watch their grief but also their recovery," Murphy told CNN. "It just makes me realize that you have to do everything to live every day without expectations for what comes next."