After hugging and handshaking and high-fiving his way through his Centennial house late last night, Tom Sullivan stood at the front door in a gray blazer and rumpled blue jeans and finally allowed himself to think about his son. It had been six years and nearly four months since Alex was murdered in an Aurora theater with 11 others, and now the 62-year-old had just scored an upset win for Colorado’s House District 37 seat.

“I think what I did is something any father would do for their child,” Tom told me as he choked back tears and his campaign team celebrated on the lawn. “I’m going to make a difference for people like Alex and for families like mine. I don’t have all the answers, but I know I have courage and determination.”

It was a surreal night at the Sullivan home, where Alex’s photos hang on walls and an upstairs closet is filled with condolence cards from around the world. When Alex was murdered on his 27th birthday in 2012, Tom was an employee with the United States Postal Service, an Air Force veteran who was looking forward to retirement and spending more time with his family.

After his son’s murder, Tom turned himself into perhaps Colorado’s most effective proponent of gun-safety laws. He went to rallies, met then-President Barack Obama, and visited the state Capitol more than 20 times to testify about pieces of gun control legislation. To put a face to his pain, Tom created a postcard with five photos of Alex at different ages and gave it to lawmakers. Printed below the photos, in block type, were the words “Alex Sullivan Murdered Aurora Theater Massacre 7-20-2012.”

“Politicians can ignore me, but I’ve dared them to ignore him,” Tom told me this past summer when I was reporting a profile of him for 5280. “Please don’t just say my son died. Alex was not taken. He was not lost. He did not pass away. My son was murdered.”

Sullivan and his team knocked on tens of thousands of doors in the 37th District after announcing his candidacy in February—running on a Democratic platform that included gun control, infrastructure, and jobs as tent pole issues. “He’s taken [his] grief and channeled it into a constructive effort,” Governor John Hickenlooper told me in July. “Tom’s convictions are so deeply held. He’s spent so much time, not just thinking, but feeling. That creates a different type of person. There’s a depth in him you don’t see very often in life.”

On Tuesday night, friends and supporters packed into the living room to watch election results with Tom and his wife, Terry, a bus driver for the Cherry Creek School District. As results showed Tom holding roughly a six-point lead over Republican incumbent Cole Wist, he moved to the backyard and stood in the cold. Six years earlier, his yard had been flooded with friends and family mourning his son. Fewer than four months ago, on July 20, he’d sat here in the middle of the night, waiting quietly as the minutes crept toward the anniversary of his son’s murder.

Now he was smoking a Brick House cigar, waiting for the final vote tally, for the call that said he’d flipped a deeply red, suburban state House district that had never elected a Democrat.

“It’s happening,” his campaign treasurer whispered.

The call came before midnight. Tom raised his right arm into the air and Terry wrapped her arms around her husband. She buried her face into his neck and kissed his cheek. “I’m so proud of you,” she said, crying. Friends screamed and hugged. His campaign manager was outside, doubled over, hands on his knees, smiling.

“You need to call your mom!” Terry told her husband.

Tom went upstairs to change for his election party at an Arapahoe County hotel. In front of the closet where the condolence cards are stored, he pulled out his phone and dialed his mother’s number.

“Hi!” he said. “We won!”

When Tom reemerged, his wife smoothed the lapels on his sports coat. Tom hugged his daughter.

“Good job, Dad.”

“I love you.”

“Ooooohhhh! We did it!” Terry screamed.

With his campaign staff waiting outside, Tom stopped at the door. It was Independence Day weekend in 1992 when the Sullivans moved into this house, when Tom told his six-year-old son that this would be his place to sell someday. Nearly 20 years to the day, it became a place of unspeakable grief. On this night, there was laughter.

“When my children were born, I looked into their eyes and realized I needed to be better,” he told me. “I needed to be stronger and smarter and funnier. I worked every single day at those things. The only thing I wanted to make sure of was that my children are proud of me.

“Other people are going to do what I did. People will see this and know you don’t have to sit idly by and accept what is happening. Maybe I can be that example: If you put in the work, if you do what’s right, you can change a community.”