At the past three Democratic conventions, only one presidential nominee mentioned the scourge of gun violence. Eight years ago in Denver, Barack Obama devoted a single sentence to the subject in his 5,000-word acceptance speech.

This year’s convention is shaping up very differently.

Shooting survivors, mothers of shooting victims and gun-safety activists took turns at center stage in this week’s Democratic National Convention here. And the duo atop the party’s ticket — presidential candidate Hillary Clinton and her running mate, Sen. Timothy M. Kaine (D-Va.) — have put the fight for tougher gun laws at the heart of their campaign for the White House.

By spotlighting gun control during their party’s biggest showcase, Democrats are marking a significant evolution in presidential politics.

For the past two decades, Democrats have been timid and even paralyzed when it comes to guns, afraid of agitating the powerful gun lobby and alienating owners of firearms. But several years of tragedies — one horrific mass shooting after another, coupled with the spate of police shootings — have presented what Democrats see as a political opening to appeal to suburban women in particular with calls for stricter gun regulations.

Mothers that have lost children to gun violence shared their stories and gave their support to Hillary Clinton during the second day of the Democratic convention in Philadelphia. (The Washington Post)

“We’ve crossed a watershed moment,” said Sen. Chris Murphy (D-Conn.), who has been a vocal gun-control advocate since the Sandy Hook Elementary School massacre in 2012 that killed 26 young children and educators in his home state.

“I’m really excited to be at a convention where Democrats are going to state loudly and clearly that this is a bedrock issue for our party,” Murphy said. “There are a lot of people who were fighting very lonely battles for a long time, and this is going to be a unifying moment for our party.”

But the Democrats’ push on gun issues has prompted a fierce rebuttal from the National Rifle Association, which has strongly endorsed Republican nominee Donald Trump and has begun a multimillion-dollar advertising campaign against Clinton through its political arm.

“The NRA has a higher favorability rating than Hillary Clinton, and voters do not trust Hillary Clinton to tell the truth on any issue, including her support of extreme gun-control measures,” NRA spokeswoman Jennifer Baker said. “We look forward to exposing Hillary Clinton’s lies about her support of extreme gun control.”

The four-day Democratic convention has been choreographed to create moments that play to voters’ emotions. They include the appearance Tuesday night of the “Mothers of the Movement” — women who lost sons or daughters to violence, including in encounters with police.

On Wednesday, former congresswoman Gabrielle Giffords, who survived a 2011 assassination attempt in her Arizona district, and her husband, astronaut Mark Kelly, will address delegates. The couple, both gun owners who see themselves as political moderates, are leading gun-safety proponents and Clinton backers.

“It’s not 1994 anymore,” Kelly said, referring to the midterm elections in which scores of congressional Democrats were swept from office, in part for backing then-President Bill Clinton’s gun control measures. “It’s a new time ... This is a topic that’s on people’s minds. People are tired of it. A majority of Americans really support some common-sense change.”

Gabrielle Giffords, center, and her husband, Mark Kelly, appeared in January with Hillary Clinton at a rally in Ames, Iowa. Giffords was severely wounded by a gunman in 2011. (Melina Mara/The Washington Post)

The program presented a stark contrast to last week’s Republican National Convention in Cleveland, where Trump presented himself as “the law and order candidate” and other speakers spoke forcefully in defense of law enforcement.

Just as the Democrats are now confident fully promoting gun control, the Republicans remain fierce defenders of the Second Amendment. The NRA’s top lobbyist, Chris Cox, was given a prime-time convention speaking slot, which he used to cast the debate over access to firearms as a civil rights issue.

“As much as we don’t like to think about it, we live in dangerous times,” Cox said. “We’re worried, and we have reason to be. Because our government has failed to keep us safe. You have to be able to protect yourself and your family.”

Since early in her campaign last year, Hillary Clinton has spoken out forcefully about gun control and vowed to take on the NRA. Clinton friends said she was personally moved by meeting families of shooting victims.

“This is about conviction more than calculation,” said strategist Paul Begala, who advises a pro-Clinton super PAC. “This is just one of those things that has moved Hillary’s heart. You could see on the campaign trail how this was affecting her.”

Clinton’s focus had political benefits in the primaries. The move helped her position to the left of Sen. Bernie Sanders of Vermont, who has a mixed voting record on gun issues. Clinton’s advisers said she would continue this approach, believing guns to be a winning general-election issue.

“Hillary Clinton has a lifelong track record and commitment to reducing gun violence and taking on the gun lobby,” Clinton spokesman Jesse Ferguson said. “She’s never backed down from that and won’t in this campaign or in the White House, and she has a running mate who shares that drive.”

“Hillary is one mother who can ensure our movement will succeed,” said Sybrina Fulton, the mother of Trayvon Martin, a Florida teen fatally shot in 2012 by a neighborhood watch volunteer.

There are dangers for Clinton. As she tries to cut into Trump’s lead with white working-class men in such places as Ohio and Pennsylvania, her position on guns could prove polarizing.

So could her association with leading figures from the gun-control movement. Former New York mayor Michael R. Bloomberg, one of the nation’s most identifiable and divisive advocates, is to appear at the Democratic convention and formally endorse Clinton.

The billionaire media mogul, who ran for mayor as a Republican and later became an independent, has spent tens of millions of dollars bankrolling campaigns to toughen gun laws, among other priorities, such as immigration.

The Clinton team points to data suggesting that women in suburban parts of battleground states such as North Carolina, Ohio and Virginia can be persuaded to back Clinton because of her stance on guns. Public polls consistently show that a sizable majority of Americans favor expanded background checks on gun purchases and restrictions on the sale of semi-automatic assault weapons.

In Senate races in New Hampshire, Ohio and Wisconsin, Democratic challengers are attempting to use the repeated failure to pass significant gun laws against Republican incumbents.

Virginia Gov. Terry McAuliffe (D), who ran aggressively in 2013 on a gun-control agenda, said it is smart politics for Clinton and other Democrats to appeal to suburban voters.

“People have leaned in hard on this issue in this year’s election, and rightfully so,” McAuliffe said. “People have had it. They’re sick of the politics around it, they’re sick of politicians being scared to death of the NRA, and they want us to stand up and fight.”

Clinton signaled she was going all in on guns with her selection of Kaine, a senator from Virginia, as a running mate. He has pushed for tougher gun laws for more than a decade, first at the state level and more recently on Capitol Hill. His leadership as governor after the 2007 Virginia Tech massacre — when he signed an executive order to keep guns out of the hands of the mentally ill — was considered a highlight of his governorship.

When Clinton and Kaine appeared together for the first time as running mates Saturday in Miami, Kaine recounted his experiences guiding his state through tragedy. He said Clinton’s plan to overhaul gun laws is “kind of emotional for me” and laid out a litany of measures they hope to enact together.

Then he mused about the NRA, which is headquartered in Northern Virginia, and all but dared the group to take him and Clinton on.

“Now, folks, I know the NRA,” Kaine said. “They campaigned against me in every statewide race that I’ve ever run. But I’ve never lost an election ... I don’t mind powerful groups campaigning against me. That just is like an extra cup of coffee to me, folks.”