Washington (CNN) Nearly a year after a gunman massacred 17 students and staffers at a Parkland, Florida, high school, the political landscape on guns has shifted.

Dozens of lawmakers endorsed by the gun-safety group Everytown for Gun Safety now hold seats in the US House -- many part of a freshman wave that helped Democrats seize control of the chamber in November's midterm elections. More than 20 states have passed some form of gun regulation in the last year, according to the Giffords Law Center to Prevent Gun Violence. And a growing number of companies are risking customer backlash to link their brands to the gun-safety movement.

Gun-control advocates say nationwide student protests after Parkland -- and the grim succession of mass shootings that have followed in the year since -- all have spurred the further shift in gun politics. And they say a strategy adopted years ago -- to follow a trail blazed by same-sex marriage advocates and take their fights to the states and corporate America -- is paying off.

In the coming year, the gun debate could be thrust into the center of the looming 2020 presidential campaign like never before.

Former New York Mayor Michael Bloomberg, one of the largest financial benefactors of the gun-safety movement, is considering entering the Democratic presidential primary. One early 2020 contender -- New York Sen. Kirsten Gillibrand, who once earned an A-rating from the National Rifle Association as a moderate Democrat representing an upstate House district -- already has spent part of her campaign rollout explaining her evolution on the gun issue to an increasingly progressive Democratic electorate.

"We're heading toward a new era on guns," said Jim Kessler, executive vice president for policy at the centrist think tank Third Way and a former aide to Senate Minority Leader Chuck Schumer of New York. "I think the tables have turned on the NRA. The gun-safety organizations are just better and smarter than they used to be. They have a lot more resources than they have in the past."

In House races last year, groups and candidates promoting gun control spent an estimated $23.6 million on television campaign ads -- more than three times the amount spent on ads opposing gun control, according to a Kantar-CMAG analysis prepared for CNN. That's a stark reversal from the 2014 midterms when anti-gun control ads outnumbered gun-control spots by nearly 5-to-1.

Last year, the National Rifle Association's spending in federal races dropped sharply, following a record $54 million in 2016 contests, including $30 million to elect pro-gun President Donald Trump, according to the non-partisan Center for Responsive Politics.

"Gun safety is no longer the third rail of American politics," said John Feinblatt, president of Everytown, a Bloomberg-aligned group that plowed $30 million into the 2018 midterm elections for Congress. "We've buried that myth."

In one of the latest examples of the growing corporate activism on guns, Blake Mycoskie, the founder of the California-based Toms shoe company, heads to Capitol Hill this week to deliver more than 700,000 postcards. They urge lawmakers to pass one of the first bills introduced by the new Democratic majority in the House: a measure that would impose background checks on virtually all gun sales.

State battles

Bloomberg, who Forbes estimates is worth nearly $50 billion, launched Everytown partly in response to a 2012 mass shooting at a Sandy Hook Elementary School in Connecticut, where 20 young children and six adults died. Despite weeks of intense debate on Capitol Hill, congressional efforts on guns stalled.

Feinblatt said Everytown took a cue from the architects of the marriage-equality movement, which chipped away at state restrictions on same-sex marriage until scoring a historic victory in 2015 when the Supreme Court legalized gay marriage nationwide.

"The gun-safety movement did the same thing and is racking up win after win across the country in red, blue and purple states," he said.

Gun-control activists have helped pass background-check ballot initiatives in Washington and Nevada, along with a slew of new laws to disarm domestic abusers and allow family members and law enforcement officials to petition courts to temporarily remove firearms from people deemed a threat to themselves or others.

In Florida, then-Gov. Rick Scott, a Republican, signed bills last year, in the wake of Parkland, raising the minimum age to purchase a gun to 21 from 18 and imposing a three-day waiting period on buying firearms. In neighboring Georgia, Democrat Lucy McBath, a gun-control activist who lost her son to gun violence in 2012, captured a Republican House seat once held by former House Speaker Newt Gingrich following $4 million in spending on her behalf by Everytown.

The group also saw 2018 wins in Nevada and Michigan, where Everytown spent $760,000 backing the campaign of Michigan's new Gov. Gretchen Whitmer. It said it spent $2.8 million supporting Steve Sisolak in Nevada, the first Democrat elected governor there since 1994. Sisolak defeated Republican Adam Laxalt, who as Nevada attorney general had opposed a 2016 Bloomberg-backed ballot initiative expanding background checks in the state.

Both states are crucial to Democrats' presidential ambitions: Michigan narrowly backed Trump in 2016 after going for President Barack Obama four years earlier. And Nevada, a perennial presidential swing state, hosts the West's first Democratic nominating contest in 2020.

Everytown's activism means "no candidate for president can go into those states and not talk pretty muscularly about the issue of gun safety," Feinblatt said.

Several already have delivered impassioned calls to action against gun-rights forces.

At a CNN town hall last month , California Sen. Kamala Harris, who is seeking the Democratic presidential nomination, lamented the failure of Congress to act on expanded background checks after Sandy Hook. She said lawmakers should have been forced to examine the autopsy photos of the "babies" killed at the school.

At her presidential campaign announcement Sunday, Minnesota Sen. Amy Klobuchar, declared she was "not afraid to join the vast majority of Americans ... to stand up to the gun lobby" and advocate for universal background checks.

Bloomberg recently told the Associated Press that he will decide on a presidential bid by month's end. Through his activism on gun-safety issues, Bloomberg has built a substantial political operation.

Everytown officials say it and its affiliates have 5.7 million supporters. In the last six months alone, the former mayor has attended 17 events in 15 states with volunteers from Moms Demand Action, Everytown's grassroots arm, his aides say.

"No one has done more to lead on gun safety than Mike," his advisor Howard Wolfson said in a statement. "Guns would undoubtedly be central to a Bloomberg campaign."

Under scrutiny

The NRA faces its own tests in the months ahead.

The organization is under increased scrutiny from Capitol Hill after alleged Russian spy Maria Butina pleaded guilty last December to attempting to infiltrate the association and other conservative groups before and after the 2016 election. Last week, two Democratic lawmakers, Maryland Rep. Jamie Raskin and Rhode Island Sen. Sheldon Whitehouse wrote to the NRA, demanding it provide more information about its activity to help Trump.

Advocacy organizations, including a gun-control legal group founded by former Arizona congresswoman and shooting victim Gabby Giffords, have filed complaints with the Federal Election Commission, alleging the NRA illegally coordinated its political advertising with Trump's 2016 presidential campaign and other Republican candidates. Those complaints followed media reports that raised questions about the NRA's relationship with what appeared to be shell companies purchasing ads.

Campaign-finance laws bar outside groups from coordinating their spending activities with federal candidates.

"The NRA complies with all election laws and any suggestion to the contrary is false," NRA spokeswoman Jennifer Baker said in an email to CNN.

And the NRA has argued in an ongoing lawsuit against New York state officials that it could be forced to curtail its operations if New York regulators persist with a crackdown that threatens its insurance and banking relationships.

To be sure, gun-rights groups have had gains in the last year, particularly in red states. NRA officials say 84% of the candidates it endorsed at the state level in 2018 won their elections.

A recent law in Wyoming allows individuals to carry concealed weapons into places of worship. And last month, South Dakota's newly elected Republican Gov. Kristi Noem signed her first bill into law: an NRA-backed measure that allows residents and visitors to carry a concealed handgun without first acquiring a permit.

At the federal level, an ardent gun-rights advocate, Republican Marsha Blackburn, won an open US Senate seat in Tennessee last November. Two other Republicans favored by the NRA, Josh Hawley in Missouri and Mike Braun in Indiana toppled Democratic incumbents, helping expand the GOP's majority in the Senate.

Those Senate victories have strengthened the NRA's firewall against any efforts in Congress to restrict access to guns, Baker said.

"With (House Speaker) Nancy Pelosi and her anti-gun minions in control of the House, we will see an uptick in PR stunts as the House passes every extreme gun-control measure under the sun," Baker said.

"But the fact remains: They do not have 60 votes in the Senate or an anti-gun President in the White House, so their theatrics will be geared towards fundraising and establishing the most liberal records for the 2020 primary election instead of doing their jobs."

NRA officials say the focus on the Senate -- where Republicans have retained their power to confirm Trump's judicial picks -- already has paid off with the Supreme Court's recent decision to take up a gun-rights case for the first time since 2010.

That case centers on whether a New York City gun law, restricting where licensed handgun owners can travel with their firearms, violates the Second Amendment. By tackling the issue, the high court's newly reinforced conservative majority "may finally re-energize a Second Amendment that has been neglected for too long," the NRA said in a statement.

The court will hear those arguments in the next term, which starts in October.

And despite recent gains by gun-control advocates, few political observers doubt the NRA's ability to rapidly fill its coffers as the 2020 presidential contest heats up. In a video last week, NRA spokeswoman Dana Loesch singled out the candidacy of Harris, a former California attorney general, as representing an "existential threat" to the Second Amendment.

Loesch then urged viewers to donate to the NRA, which she called "the one organization powerful enough to disrupt the socialist plan to disarm America."

Smart business?

For many people who joined the gun-control movement in the past year, Parkland was a defining moment. Survivors led hundreds of thousands of protestors in March for Our Lives rallies around the country a little more than a month after the shooting.

And some businesses began to reexamine their policies. Dick's Sporting Goods, for instance, removed assault-style rifles from its Field & Stream stores and stopped selling guns to anyone younger than 21. Walmart raised the age to purchase firearms to 21 from 18. Last September, the iconic denim brand Levi Strauss pledged $1 million to groups working to curb gun violence and partnered with Bloomberg to build a coalition of business executives committed to working on gun control.

As a father, Mycoskie, the founder of Toms, said he had been shaken by the carnage in Parkland. Last November, however, the violence struck closer: 12 people were shot dead at a bar in Thousand Oaks, California, just 15 minutes from his home.

The following morning his wife, Heather, called him as he headed into Toms headquarters and said, "'I'm scared, and I don't want to take our (four-year-old) son to school today,' "Mycoskie recalled in a recent interview.

"She was very emotional and basically said that somebody has to do something about this."

Within weeks, Toms had committed $5 million to groups working on gun violence, including Moms Demand Action for Gun Sense, a grassroots arm of Everytown for Gun Safety. He launched a postcard-writing campaign on the Toms website and in its stores, urging Congress to pass universal background checks.

Mycoskie, 42, is no stranger to corporate activism. He started the shoe brand in 2006 with a mission of philanthropy and has donated shoes to more than 86 million people so far. The Toms eyeglass brand helps finance eyesight restoration; proceeds from its coffee-roasting operation help supply clean water in poor communities.

Jumping into the gun debate was a new risk, however. For starters, the company's internal polling shows its customer base divides equally between Republicans and Democrats, Mycoskie said.

And corporations taking gun-safety stands have faced a backlash from gun owners and conservatives. Just last year, Georgia's Republican-controlled legislature blocked a tax break on jet fuel after Delta ended a discount-fare program with the NRA. (A few months later, then-Gov. Nathan Deal, a Republican, took executive action and halted collection of the tax.)

"What these corporations and billionaire politicians fail to realize is that the Second Amendment is in the hearts and minds of the American people," said Andrew Arulanandam, another NRA spokesman.

But for some companies, the benefits of reaching a new segment of shoppers could outweigh the downsides.

Millennials, defined by the Pew Research Center as those born between 1981 and 1996, are poised to overtake Baby Boomers as the nation's largest living generation this year. CNN's 2018 exit polling shows the highest level of support for gun control measures -- 66% -- among younger voters between the ages of 18 to 29.

These generational differences underscore the "upside potential" on the gun issue for brands that appeal to a younger customer base, said Roger Beahm, executive director of the Center for Retail Innovation at Wake Forest University's School of Business.

"Corporations have a finger in the wind and they are looking down the road -- what's the likely direction in the future?" added Robert Spitzer, a political scientist at the State University of New York-Cortland, who has written five books on gun policy.

"Many have come to the conclusion that this a good step for them, precisely because it burnishes their social responsibility model," he said.

Mycoskie said Toms draws on mothers on the "older edge" of the millennial generation for the biggest share of its customers, and, so far, the reaction to its gun activism seems mostly positive. The company's review of social media found that about 75% of customers back the move, and about 12% oppose it strongly and say they will boycott Toms brands.

"In theory, we lost about 12% of our customers, which is a big number in a business our size," he said.

But Mycoskie said direct, e-commerce sales are up about 21% -- as people visit the website site to join the postcard campaign and start shopping while there. It's too soon, he said, to gauge the effect on wholesale orders, many of which were placed months before his background-check campaign began.

"We knew going in that if it got positioned as a highly political, left-leaning act that it would be very bad for business," he said. "But we felt like we had to take that risk because the other risk we have is that we are a brand that is completely built on standing for something."

"When things like this happen and we don't act," he said, "then there's also a large group of our customers who will lose faith in us."