DES MOINES, Iowa (AP) — Democratic presidential candidates on Saturday placed responsibility for inaction on gun violence in the hands of President Donald Trump and the National Rifle Association, in the face of broad national support for some gun control measures.

"If most Americans insist that something be done and it doesn't happen, it means we need fundamental reform," Pete Buttigieg, the mayor of South Bend, Indiana, said at a presidential forum on gun violence in downtown Des Moines.

The forum comes a week after a pair of mass shootings in El Paso, Texas, and Dayton, Ohio, shook the nation and reignited a debate surrounding gun rights in America. Seventeen candidates were due to speak and answer questions from members of the gun control group Moms Demand Action in the crowd, some of whom teared up while describing the ways gun violence had affected their families.

New York Sen. Kirsten Gillibrand, in response to a question on how to avoid stigmatizing mental illness when the president has repeatedly highlighted that issue in response to mass shootings, called Trump a liar. Most people with a mental illness are not violent.

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"It's just President Trump lying to the American people again, being inauthentic about what the problem is ... trying to distract, and trying not to take responsibility for what is happening in this nation," she said.

A number of candidates have released gun control policies in the week since the shootings. On Saturday, the Democrats largely agreed on the broad contours of the policy debate, emphasizing the need to close background check loopholes, ban assault weapons and fund research into gun violence. Most of the candidates also called on campaign finance reform as a solution to combat the influence of the NRA on elections.

California Sen. Kamala Harris added her voice to the growing number of candidates calling on Walmart to stop selling guns — "I do believe that," she said — but she also pressed strongly for background checks for potential gun buyers. Walmart is one of the biggest retailers of firearms in the United States, and the El Paso shooting occurred at a Walmart store.

"We need background checks. Let's just start with that," she said. "And we need people to be, as I've said, responsible in the way they are selling guns. So it's not about everyone needs to stop selling guns. But we absolutely need to have checks and balances on it."

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Harris joined Vermont Sen. Bernie Sanders, Massachusetts Sen. Elizabeth Warren, New Jersey Sen. Cory Booker and former Housing Secretary Julian Castro in calling for the big-box store to end its gun sales. Warren, who called a day earlier for Walmart to stop selling guns, told Americans on Saturday to put pressure on the company by taking their business elsewhere.

"It's up to every Walmart customer who worries about the safety of her children, of her neighbors, of her friends, of people across this country to say, 'I've got choices on where I spend my money ... and I'd rather do my banking in line with my values," she said.

A Walmart spokesman has said the company is conducting "a thorough review of our policies" after the shooting.

A trio of more moderate candidates — Ohio Rep. Tim Ryan, Montana Gov. Steve Bullock and Minnesota Sen. Amy Klobuchar —called on gun owners to get involved in the gun control effort.

"If we can ever look at this issue as not a political issue but a public health issue, we know what to do. The majority of gun owners, the majority of NRA members, all of us think universal background checks make a heck of a lot of sense," Bullock said, noting he uses guns and has taken his son hunting.

A 2017 Pew Research Center poll showed a slight majority of NRA members — and more than three-fourths of gun owners polled — support stronger background checks.

Buttigieg, who recently dealt with a fatal police shooting of a black man in his home city, was asked how he'd address the issue of police shootings. He proposed deescalation training, equipping police officers with nonlethal weapons and demanding more accountability so that "officers who do the wrong thing live with justice."

But a number of the candidates expressed optimism that there was momentum in favor of gun reform because of the growing pressure from the public on lawmakers to act.

"There's a tipping point that's been reached. I feel it out there," Klobuchar said.

Warren released a sweeping gun control agenda on Saturday before the event, starting with a trio of actions she vowed to immediately take if elected — including an expansion of background checks accomplished by redefining the federal standard for those "engaged in the business" of gun sales — and continuing with a long list of legislative priorities.

Chief among Warren's longer-term gun control goals, she explained in a Medium post about her plan, are the creation of a federal license for any firearm purchase, exponentially higher taxes on guns and ammunition sales, and a one-gun-per-month purchasing limit.

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Associated Press writers Will Weissert in Des Moines and Elana Schor in Washington contributed to this report.

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