Twenty minutes into his state of the state address last April, Minnesota Gov. Tim Walz turned to the issue of gun violence. The state legislature was considering proposals to impose universal background checks for buying firearms and a red-flag law that would temporarily bar people from buying guns if they presented a danger to themselves or others.

Walz threw his support behind both measures.

“I’ll go ahead and put my credibility up against anyone on this issue,” Walz told the lawmakers gathered at the Minnesota House of Representatives. “I’m a veteran and I’m a hunter. And for many years I was one of the best shots in Congress, and I got the dang trophies to prove it.”

“But I’m sick and tired of talking about that,” Walz added. “Because I’m not just a veteran, not just a hunter, not just a gun owner — I’m a father. And for many years I was a teacher. And we all know damn well weapons of war have no place in our schools, in our churches, in our banks, for anyone who wants to live in peace.”

The comments met with ringing applause. The following month, Walz signed the measures into law.

When Kamala Harris, the Democratic presidential nominee, chose Walz as her running mate Tuesday, she elevated an unusual voice for gun reform — a lifelong firearm enthusiast who changed seven years ago from a darling of the National Rifle Association into a champion for gun safety.

Guns have played an important role in Walz’s life, personally and professionally. He grew up hunting in rural Nebraska and then served for 24 years in the Army National Guard.

In the years after his first election to the U.S. House in 2006, the NRA consistently awarded him an A rating for his pro-gun positions and endorsed him repeatedly in elections.

Walz was among 304 members of Congress — mostly Republicans — to sign on to a friend-of-the-court brief in the landmark 2008 case of District of Columbia v. Heller, urging the U.S. Supreme Court to overturn Washington’s tight restrictions on handgun possession and its prohibition on keeping loaded handguns in the home for self-defense.

“A ban on handguns is both unusual and unreasonable,” the brief says, later adding: “The District’s law-abiding citizens are deprived of handguns that are commonly kept by law-abiding persons throughout the United States for lawful defense, which exacerbates the District’s high murder rate.”

The Supreme Court’s ruling in the Heller case established for the first time that the Second Amendment right to bear arms applies to individuals rather than just militias — a decision that laid the basis for sweeping constitutional challenges to gun safety laws.

But Walz changed course in 2017, after a lone shooter fired more than 1,000 rounds into the crowd at the Route 91 Harvest Music Festival in Las Vegas, killing 60 people and injuring 850 others. He donated $18,000 he had received from the NRA to a veterans’ charity.

“The country’s changed on this. We’ve changed. The situation has changed and I along with it as a leader,” Walz said in an interview explaining his about-face. “I’m a staunch supporter of Second Amendment rights to own firearms. ... But I also recognize the need to have some common-sense changes in this. I reject the notion that it’s one or the other. Those folks out there who are responsible gun owners ― their hearts are breaking every time you see one of these shootings.”

When a mass shooter killed 17 people and injured 17 more with a semiautomatic rifle at Marjory Stoneman Douglas High School in Parkland, Florida, the next year, Walz threw his support behind an assault weapon ban.

Since being elected governor of Minnesota in 2018, he has grown more vocal on the issue. In addition to the reforms he signed last year, which also included a sizable investment in community violence prevention, earlier this year he signed laws boosting the penalty for straw purchases and banning binary triggers (devices that allow a shooter to fire both when pulling and releasing the trigger).

Walz cites his own gun ownership to bat away the notion that safety laws make it harder for people to keep buying guns.

“You are not going to frame this that this is taking your guns, because I’m going to frame it that you’re not sticking up for our children,” Walz said at a news conference last year when the Minnesota Legislature was debating the red-flaw law and universal background checks.

Gun reform groups, including Giffords Law Center and Everytown for Gun Safety, applauded Harris for picking a hard-charging champion of firearm safety laws.

“Young people are fired up like I’ve never seen to vote in this election, and Governor Walz is turbocharging that,” David Hogg, a survivor of the Parkland shooting and co-founder of the March for Our Lives Action Fund, said in a statement, going on to describe Walz as “a gun safety champion who can bridge the divide.”

The NRA, however, has long soured on Walz. Randy Kozuch, the chairman of the NRA Political Victory Fund, called the governor a “political chameleon” after Tuesday’s announcement, saying in a statement that the Democratic vice presidential pick “purported to be a friend of gun owners to receive their support in his rural Minnesota district.”

“Once he had his eyes set on other offices, he sold out law-abiding Minnesotans and promoted a radical gun control agenda that emboldened criminals and left everyday citizens defenseless,” Kozuch’s statement says. Kamala Harris and Tim Walz cannot be trusted to defend freedom and our Constitutional rights.”

Walz is accustomed to the criticism.

“When I first started in Congress, I had an A rating from the NRA,” Walz said at last year’s state of the state speech. “I have straight Fs now. I sleep just fine at night.”