Sen. Elizabeth Warren of Massachusetts pledged to sign comprehensive gun control legislation in her first 100 days in office if she's elected president. Sen Kirsten Gillibrand of New York rallied Americans to challenge Senate Republicans holding up gun control legislation, while gun owner and Montana Gov. Steve Bullock urged people to take on the National Rifle Association. Former Housing and Urban Development Secretary Julian Castro took the issue past simple criminality, noting that "police violence is gun violence too."

They were among 17 Democratic presidential candidates appearing at an event Saturday in Des Moines, Iowa. And while it's normal for presidential hopefuls to spend time in the nation's first presidential caucus state, it's less common for people running for president to be so unabashed in their pledges to put limits on guns and to challenge one of the most powerful political forces in America.

"What we have now is that the memory of 1994 may be fading for Democrats," says Ronald Schurin, a political science professor at the University of Connecticut, referring to massive Democratic losses in the House of Representatives, following an aggressive NRA campaign against lawmakers who voted for the Brady Bill gun control legislation.

Meanwhile, there are more recent memories that are affecting the public at large and the candidates seeking to represent them, he notes: the mass shootings at an elementary school in Newtown, Connecticut and a high school in Parkland, Florida, and the ones last weekend in Dayton, Ohio and El Paso, Texas.

"After every tragedy, there is a burst of pro-gun control enthusiasm, and it dissipates after awhile because people who feel really strongly about this issue in a permanent, ongoing sense tend to be on the other side of the issue," Schurin adds. But now, as the NRA deals with its own financial and other internal problems, "perhaps they are a little less afraid of the NRA than they were in the past," he says.

Igor Volsky, author of the book "Guns Down: How to Defeat the NRA and Build a Safer Future With Fewer Guns," says that he has noticed a shift among Democratic candidates, who not only don't shy away from the issue but embrace it.

"Part of my job is to talk to the campaigns and to talk to people who may be the future leaders of our country," says Volsky, executive director of Guns Down America Action Fund. "And it's fairly competitive in terms of, what can we do? How can we be bolder? How can we distinguish ourselves? There is some level of competition on this issue," Volsky says.

Early presidential contests are coincidentally in states which have large rural areas and where hunting is popular: Iowa, New Hampshire, Nevada and South Carolina. But even that dynamic has changed. Giffords, a gun violence prevention group named for the former congresswoman, Gabby Giffords, who survived a gunshot to the head in 2012 as she met with constituents in her Arizona district, has planned an event in Nevada two months from now, and already, nearly every Democratic candidate has committed to attend, says Giffords' Executive Director Peter Ambler.

"The politics has swung decisively" toward more gun control, Ambler says. Young people, as well as residents of increasingly urbanized states – including Texas and Arizona – are driving the renewed focus on the issue, he says.

On Saturday, the vast majority of the two dozen Democratic presidential nominees made the case for new gun laws at an all-day forum sponsored by Everytown for Gun Safety Action Fund, Moms Demand Action and Students Demand Action. As attendees held up photos of loved ones they have lost to gun violence, candidates competed for who would be the strongest and most effective advocate for policies to reduce gun violence.

Former Rep. Beto O'Rourke appeared by video, since he was in his home town of El Paso, where 22 people were gunned down at a Walmart last weekend. Sen. Cory Booker of New Jersey, who has been a vocal supporter of new gun safety and gun control laws, was attending a memorial service for a family member and could not attend, his campaign manager, Addisu Demissie, said in a tweet.

Sen. Amy Klobuchar talked about the connection between guns and violence against women, promising to get rid of the "boyfriend loophole," which excludes many unmarried romantic partners from laws banning gun ownership in cases of domestic abuse. South Bend, Indiana Mayor Pete Buttigieg noted that mass shootings are "usually happening to people of color."

Sen. Bernie Sanders — noting that his home state of Vermont had no gun control at all until last year — called for a ban on the sale and distribution of assault weapons. O'Rourke called for a litany of new laws backed by many of his primary competitors, including national licensing of guns, "red flag laws" keeping guns from people deemed to be mentally ill, and closing loopholes that allow people to get guns without passing background checks first.

Former Vice President Joe Biden called for repealing a law that protects gun manufacturers from lawsuits and said the Second Amendment has been wrongly construed to mean anyone can own any kind of gun to protect against government tyranny.

"These guys will tell you the tree of liberty is watered with the blood of patriots. Give me a break," Biden said. "Carry concealed weapons? Come on. Can you go out and buy a flame-thrower? Can you go out and buy an F-15?" Biden asked the crowd.