Tim Walz was in the thick of a crowded Democratic primary for governor of Minnesota in August 2017 when he appeared at a sports and outdoor show known as Minnesota’s “finest hunting event.”

As a congressman representing a rural swath of southern Minnesota, Walz had championed gun rights — earning an “A” rating from the National Rifle Association —and often proudly sported a camo hat featuring the affirmation “NRA ENDORSED.” Butas he soughthis party’s nomination in a state that had backed the Democratic presidential nominee since 1976, Walz was equivocal when asked about access to guns.

“He tried to find a middle ground, saying he was a strong advocate but also supported common sense regulation,” said Rob Doar, senior vice president of the nonprofit Minnesota Gun Owners Caucus, a prominent gun rights group.

The moment showed howWalz went about moderating his stance on guns — slowly at first, and then seemingly all at once. Two months later, after a gunman left 60 dead at a country music festival in Las Vegas, Walz pledged to donate his previous NRA contributionsto a charity for families of fallen service members. And a mere four months after that, as the nation reeled again from a mass killing, this time at Marjory Stoneman Douglas High School in Parkland, Fla., Walz “went full-bore on gun control,” Doar said.

The shift, capped by his recent support as governor for a wave of significant gun-control bills in Minnesota, placed him squarely in line with the mainstream of the Democratic Party, which he’s now helping lead into November as the vice-presidential nominee. His evolution on guns, in a tight time frame punctuated by some of the most deadly recent shootings, illustrates the galvanizing effect of the mass-casualty events. But his change of heart also came at a time when gun-control groups began spending significantly more on candidates who shared their positions.

In his decade as a pro-gun congressman, Walz received donations totaling $18,950 from the NRA and $6,000 from the National Shooting Sports Foundation, campaign records show. After Parkland, as he prepared to go to battle with the NRA, which had earned a reputation as a grassroots juggernaut that could make or break a political career, he wrote on Facebook: “I expect them to start spending heavily to defeat me.”

Instead, that year marked a turning point, as gun-control groups outspent the NRA and other firearms organizations amid an outcry over gun violence. The political arm of Everytown for Gun Safety, the group founded by billionaire Mike Bloomberg, invested heavily in governor’s races, helping to elect Democrat Gretchen Whitmer in Michigan and to defeat Republican Adam Laxalt in Nevada. And in the homestretch of the race in Minnesota, Everytown donated $200,000 to a pro-Walz political committee, according to campaign records.

“It’s no surprise he turned away from the NRA as the NRA turned more and more extreme,” said John Feinblatt, president of Everytown for Gun Safety. “Governor Walz has proven that he’s not afraid to stand up to the gun lobby to keep his constituents safe.”

In the days since Democratic presidential nominee Kamala Harris picked Walz as her running mate, gun rights groups have sought to remind voters of what they cast as the governor’s betrayal.

“Tim Walz is a political chameleon — changing his positions to further his own personal agenda,” Randy Kozuch, chairman of the NRA Political Victory Fund, said in a statement. The U.S. Concealed Carry Association for Saving Lives sent out an alert to members featuring a video of Walz signing gun-control legislation that it said created “onerous barriers standing in between you and your ability to protect your family.”

A spokeswoman for the Harris-Walz campaign said, “After some of the worst mass shootings in our country’s history, the governor was moved to take a hard look at the facts and decided to support common sense gun reform that would prevent future tragedies. That level of introspection is something to be commended, not critiqued.”

A lifelong hunter and former National Guardsman, Walz was active in the Congressional Sportsmen’s Caucus when he served in the U.S. House from 2007 to 2018, and he led the group during part of his time on Capitol Hill. He backed a number of bills favored by gun enthusiasts and, in 2016, Guns & Ammo magazine named him one of the top 20 politicians for gun owners.

But there were signs that Walz was not as hard line as some of his more conservative colleagues. After the mass killing at Sandy Hook Elementary School in 2012, Walz indicated he might be open to a ban on high-capacity, military-style rifles.

“What people are putting forward, looking at assault magazines, assault weapons, that should be in the discussion,” he told a Minnesota paper. “It has to strike the proper balance between the constitutional rights of law-abiding citizens versus the safety of all Americans.”

Five years later, as he campaigned for governor, he faced pressure from within his party to take a stronger position on guns. A Democratic primary opponent, Erin Murphy, made an issue of his “A” rating from the NRA and called on him to give back contributions from the pro-gun advocacy group, which he pledged to do after the carnage at the Route 91 Harvest music festival in Las Vegas in October 2017.

“We came into that race with different positions and he evolved over time,” said Murphy, who’s now the Democratic majority leader of Minnesota’s state Senate. “And I understand why, rightfully, because of what we were seeing happening.”

After the Parkland shooting in Florida in February 2018, Walz proposed an assault weapons ban. At one campaign event, he said: “My job today is to be dad to a 17-year-old daughter named Hope,” explaining that after the violence, she “woke up like many of you did five weeks ago and said, ‘Dad, you’re the only person I know who’s in elected office. You need to stop what’s happening with this.’”

Walz added: “I’ll take my kick in the butt from the NRA.”

Walz’s shift also came as gun-control groups were gaining influence and the NRA was roiled by internal feuds and corruption allegations. Between 2016 and 2022, NRA revenue fell more than 40 percent, while membership dues were down roughly 50 percent, according to tax filings. Campaign spending dropped, and legal expenses soared. The NRA’s Political Victory Fund donated just $2,000 to Walz’s Republican opponent in the fall of 2018, records show.

Gun rights groups did not mobilize in a significant way against Walz when he ran for reelection in 2022, said his Republican opponent, then-state Sen. Scott Jensen, who had backed increasing penalties on “straw” buyers of firearms who resell them to ineligible gun owners.

“The gun groups weren’t falling in love with me either even though I was stronger [on gun rights] than Tim Walz,” said Jensen, who called Walz “a very adept politician.”

In 2023, as Democrats controlled both legislative chambers and the governor’s mansion for the first time in about a decade, Walz signed sweeping gun-control legislation that expanded background checks on gun buyers and created “red flag” protections to take guns away from people deemed a danger to themselves or others.

Murphy, his onetime primary opponent, said he has proved himself a reliable partner on gun violence prevention.

“The last two years in Minnesota, we’ve passed a number of pieces of legislation that he signed into law as a result of that necessary evolution,” she said.

In late July, as Harris was nearing a decision on her running mate, Walz bragged in a social media post about getting “straight Fs” from the NRA in recent years. “And I sleep just fine,” he added.

Clara Ence Morse contributed to this report.