Former Colorado Gov. Hickenlooper, now presidential candidate, marks somber anniversary with Columbine survivors

It was sunny and warm as students walked to class at Columbine High School earlier this week, just as it was in 1999, when two boys in trenchcoats tore through the school on a killing spree. Twenty years since the horrific massacre that took the lives of 12 classmates and a teacher, the community in Colorado looks to move on -- even while looking back.

Presidential candidate and former Colorado Gov. John Hickenlooper met with survivors of the Columbine attack this week, along with other survivors of his home state’s mass shootings.

Sitting together in a circle in Denver’s First Baptist Church on Tuesday, the mood in the room was somber as the former governor talked with survivors about their guilt and long-term trauma.

"This is kind of the trauma that no one is prepared for," Hickenlooper told them, expressing the need for increased attention and expanded federal funding for mental health services for those affected by mass shootings.

"We have been insufficient and derelict in providing resources. That's something certainly I think the federal government could step in when you have these mass shootings happen so frequently -- the collateral damage to families and not just them -- first responders -- has been immense."

He said it was a moment for them all to reconnect and brush against an issue that he may make a focal point of his 2020 campaign: gun control.

Some of those in the meeting on Tuesday with Hickenlooper were even present when he signed landmark legislation placing new restrictions on firearms in 2013.

Tom Mauser lost his son, Daniel, in the mass shooting at the Colorado high school and was there to watch as the then-governor signed the new law. Tuesday, he shared a worry that he had with Hickenlooper, that there's too much emphasis on "staying strong" for survivors.

"So often after these tragedies, we have this movement -- with Columbine and others -- stay strong, be strong, look at the positive," Mauser said "People need to do that healing, but sometimes there's not enough acknowledgement of the pain that still goes on."

Hickenlooper's state has seen its fair share of the violent trauma which swirls around the gun debate; Hickenlooper was governor when James Holmes opened fire on an Aurora movie theater in 2012, killing 12 and leaving dozens more injured.

"It changes you. It changed me," the former governor said in an interview with ABC News. "It wasn't an overnight transformation, but there was that period of time it felt ... we just can't stand by with the status quo -- which is really what Republicans have been saying: 'These are just some things we just can't do anything about.' I don't think the country is willing to stay there anymore."

Hickenlooper wants to enact on the federal level many of the things done in his state in the aftermath of mass shootings: universal background checks, a ban on high-capacity magazines and raising the minimum age to buy certain firearms.

He has had a long, and at times complicated, past with the issue, and not one he came to immediately. Hickenlooper told ABC's "This Week" -- in the wake of the Aurora shootings -- that even if Holmes did not have access to guns, he would have found a way to create "horror."

"This wasn't a Colorado problem. This is a human problem," Hickenlooper told ABC News' George Stephanopoulos in 2012. "Even if he didn't have access to guns, this guy was diabolical … he would have found explosives; he would have found something. … He would have done something to create this horror."

Since then, Hickenlooper has adapted his tone, and more than once. Colorado has passed measures expanding background checks and limiting magazine sizes to 15 rounds despite furious backlash from gun rights groups. He later couched himself with Colorado sheriffs, expressing regret if he didn't fully vet the measures that he had championed, remarks some heard as distancing himself from the divisive issue.

He's not the only 2020 presidential candidate with a nuanced record on gun laws. Sen. Kirsten Gillibrand has tumbled from an "A" rating from the National Rife Association to an "F," a point of pride, she's said. She has also expressed remorse over her past pro-gun rights stance.

Sen. Bernie Sanders, of Vermont, a state friendly toward hunters and guns by rural wont, has in the past been attacked for being too moderate on gun control, especially in his early career.

Now, the tide seems to be shifting notably in the Democratic Party. Candidates for 2020 are embracing more stringent gun control with hawkish gusto, perhaps fueled in part by so many recent mass shootings across the nation. Four of the top 5 and six of the top 10 deadliest mass shootings in modern U.S. history have happened this decade.

Hickenlooper said he thinks the important thing is to unite in efforts to stop gun violence, no matter which side of the wedge you're on.

"I think whoever becomes the next president should lead that effort," he told ABC News. "I think we learn from our mistakes. ... I feel there is change that is coming. I feel we are at a tipping point, and some of the obstacles are maybe not so impossible as maybe they seemed a couple years ago."