Aurora, Colorado (CNN) Coni Sanders, the daughter of a teacher who was killed in the Columbine High School shooting, has a message for Colorado Republican Sen. Cory Gardner .

"Senator Gardner, this has to stop. We are begging on the lives of our loved ones, begging on the lives of our family for you to support this," Sanders said in a room surrounded by activists holding signs saying "gun laws save lives" and "change gun laws or change Congress."

"After so many devastating shootings, now we're asking Cory Gardner: Join us because we need you and you need us," Sanders said at a recent press conference calling on the Senate to pass background check and red flag gun legislation.

The event was organized by Everytown for Gun Safety and held at the district office of Democratic Rep. Jason Crow in Aurora, Colorado, where in 2012 a gunman opened fire in a movie theater, killing twelve people.

In the wake of mass shootings that shocked the nation in El Paso, Texas, and Dayton, Ohio, activists have worked to put pressure on Gardner with news conferences, protests and ad campaigns calling on him to support tougher gun laws at the federal level when Congress returns from its summer recess this week.

Gun control advocates argue that the politics of the gun debate have shifted in Colorado and the state is more willing to support stricter gun laws after enduring tragedies like Columbine and Aurora.

But the purple state has also seen a backlash in the face of new firearm laws and it's not just gun control advocates putting pressure on Gardner.

Gun-rights activists say the Republican senator will pay a price at the ballot box if he supports gun legislation like expanded background checks or a national red flag law -- which some Republican lawmakers in Washington have expressed support for -- which could help keep guns out of the hands of individuals deemed to be a threat to themselves or others.

"He's going to have a tough reelection, no question and the last thing he needs is a fractured base," Dudley Brown, the president of the National Association for Gun Rights and executive director of Rocky Mountain Gun Owners, told CNN in an interview.

Pressure on both sides

Gardner is considered to be one of the most vulnerable Republicans defending a Senate seat in 2020. A crowded field of Democrats, with former Colorado governor John Hickenlooper in the position of frontrunner, is vying to take him on in next year's general election.

"Supporting red flag would completely fracture the base," Brown said, predicting that if Gardner voted for or publicly came out in support of federal red flag legislation, "he will not win reelection."

After the El Paso and Dayton shootings, Gardner said in a statement on Twitter that it is "heartbreaking to see more senseless violence." He called the El Paso shooting a "case of domestic terrorism," and said, "There's no place for bigoted white supremacy in our nation."

At an event in Aspen following the shootings, Gardner again condemned white supremacy, but also said, "I don't support gun control," according to The Aspen Times.

The Gardner campaign did not make the senator available for an interview with CNN for this story and did not respond to questions about whether the senator would support or oppose expanded background check or federal red flag legislation if either came up for a vote in the Senate.

Pins and stickers advocating to stop gun violence are on display during the Gun Safety Town Hall.

Gardner has previously argued that action to address gun violence cannot infringe on constitutional rights.

"We have to prevent violence and we should protect our communities, but we can't violate the Constitution," Gardner said during a May radio interview when asked about red flag laws.

The senator has also raised questions about whether red flag legislation in Colorado is constitutional.

"I think you could possibly craft a bill to protect the Constitution," Gardner said during the same interview in response to another question about red flag laws, adding, "I don't know that you could construct it as they wrote it in 2018 or 2019," a reference to state legislative proposals.

Brown of the National Association for Gun Rights told CNN that Gardner has told him that he does not support red flag laws.

"He has voiced directly to me and to one of the more prominent sheriffs in the state directly that he is opposed to red flag laws and thinks they're unconstitutional," Brown said, adding, however, that the senator "didn't commit to voting against any specific proposals."

Weld County, Colorado Sheriff Steve Reams, an outspoken opponent of the state's red flag law, said that he has also had a chance to speak with Gardner about red flag laws.

"He has made his position clear with me," Reams told CNN, "he said he wasn't supportive of red flag legislation."

But the sheriff added, "I haven't seen him say that publicly so I can't speak on his behalf. I guess that's something you'd have to ask Senator Gardner. I don't believe he's in support of red flag laws, but your vote is what matters when you're in DC."

Activists want answers from Gardner on gun legislation

Jessica Price, who leads the Aurora group of Moms Demand Action for Gun Sense in America, said that her group has been trying to meet with Gardner to talk about gun legislation, but has so far been unsuccessful.

"We've been trying to meet with him for quite a while," Price told CNN, adding that they have met with some of the senator's staffers, but not Gardner himself. "We just haven't been able to get face-to-face time with him at all," she said.

State Rep. Tom Sullivan sponsored Colorado's new red flag law. His son Alex was killed in the 2012 Aurora theater shooting.

Moms Demand Action is part of Everytown for Gun Safety and has chapters in every state and hundreds of local groups nationwide.

The Aurora Moms group recently convened a Senate candidate forum on gun violence where several Democratic Senate contenders showed up. Price said Gardner was invited, but never responded.

"We're disappointed," Price said, "because we would like to hear from him."

A Gardner campaign official told CNN that Gardner recently spoke with several members of Moms Demand Action at a Republican picnic in Jefferson County, Colorado at the end of August.

Price hopes that Gardner can be convinced to support background checks and a strong red flag law at the national level.

"At this point we're still kind of at that persuasion stage where we'd like to hope that we could persuade him to vote for some common sense gun legislation," Price said, adding that she and others want to meet with the senator "to get some clarification on his stance."

People walk by a cardboard cutout of US Sen. Cory Gardner after the Gun Safety Town Hall in Aurora last month. Activists brought the cardboard cutout around the state on a bus tour.

A coalition of progressive organizations, including Indivisible groups in the state and ProgressNow Colorado recently organized a bus tour for a cardboard cutout of Gardner nicknamed "Cardboard Cory" in an effort to argue that the senator hasn't been showing up to public events in the state.

Gardner has argued that he is accessible to constituents. "We sit down regularly ... We've done thousands of meetings across the state," he said at a recent event, according to The Denver Post.

The senator told a reporter for CNN affiliate KDVR last month, "every chance we get to go across all four corners of the state, I'm going to continue to do that."

Gardner has hosted or attended more than 50 events across the state during the month of August, including roundtable events and parades, according to lists provided to CNN by his senate office and campaign.

A spotlight on Colorado over recess

Gun violence prevention groups have worked to put a spotlight on Gardner over the August congressional recess.

Everytown for Gun Safety and Moms Demand Action rolled out a plan to spend nearly $1 million on digital and television ads targeting key Republican senators over the recess, including Gardner in Colorado.

The gun violence prevention organization Giffords has spent nearly $750,000 on an ad campaign calling for the Senate to hold a vote on background checks with ads specifically calling out Gardner.

Former Democratic congresswoman Gabby Giffords, the co-founder of the organization and a gun violence survivor, urged a crowd at a recent gun safety town hall in Aurora to "be bold, be courageous," in the fight for stricter gun laws.

Gun control groups have even outspent the NRA in the current campaign to put pressure on the Senate to vote on gun legislation, according to the Center for Responsive Politics

Lesley Hollywood is the founder and director of Rally for our Rights, a gun rights advocacy group.

Lesley Hollywood, the founder of Colorado gun rights group Rally for Our Rights, said she believes Gardner is thoughtful and deliberative and won't be pushed into taking a stand one way or the other on gun legislation without careful consideration.

"I like to think that Cory is a solution-based person," Hollywood said, adding, "We need to be reading bills and looking at data and making informed decisions and that's what Cory does."

She predicted, however, that Gardner would not support a federal red flag law because he would find it to be unconstitutional.

"He's going to determine should we be pushing this on the federal level?" Hollywood said.

"My guess is he's going to say no, because I trust he's going to dig into this enough to realize this is dangerous legislation."

The politics of gun control in Colorado

In the 2018 midterms, Crow flipped a Republican-held congressional district in Colorado while putting the issue of gun safety front and center in his campaign.

The Democratic freshman believes that one of the takeaways from his election to Congress is that "the tide has shifted" in the state when it comes to the gun debate and there is now stronger support for action to prevent gun violence.

"The conventional wisdom in a district like mine, in a state like Colorado, is you don't talk about issues like this. I believe that was wrong," Crow said, adding, "I don't think a week goes by that I'm out in this community that I don't run into parents, teachers, students who come up to me with tears in their eyes telling me they're afraid to go to school, they're afraid to take their kids to school. That's the environment we're now raising our kids in. They've had enough. I've had enough."

Coni Sanders, who lost her father in the Columbine shooting, argued that gun violence has become a personal issue to many Coloradans as the state has endured tragedy after tragedy.

"There are so many people impacted by this now that we can't just turn a blind eye," Sanders said. "I think when it comes down to it attitudes are changing because people are realizing that nobody is safe."

Jessica Price is the president of the Aurora Moms Demand Action group.

But not everyone impacted by gun violence supports stricter gun legislation, some oppose further restrictions.

"For me, it's a pretty personal issue. I see that we've tried more gun control and all these other different approaches year after year to solve these mass shootings and none of it's working," said Patrick Neville, a survivor of the Columbine shooting and the Republican minority leader of Colorado's House of Representatives.

In the state legislature, Neville has fought against tougher gun restrictions, including the state's red flag law.

Following the Aurora shooting, the Colorado legislature passed background check legislation. This year, the legislature passed a red flag law. It will go into effect in January.

Gun control supporters argue that if Gardner doesn't support those policies at the national level he will be out of step with his own state.

But gun legislation has also sparked intense opposition in the state.

Colorado's red flag law has prompted a legal challenge attempting to overturn it. Some sheriffs have said they oppose it and have said they would be willing to go to jail rather than enforce it and a number of counties have declared themselves Second Amendment "sanctuaries" in protest against the legislation.

Neville said that he is optimistic that Gardner would oppose federal background check or red flag legislation if either were to come up for a vote in the Senate.

"He's obviously seen what's happened in Colorado," Neville said, adding that he is "really confident he'll make the right decision and do what's right for our state and the nation."