Former Massachusetts governor Mitt Romney  worked Friday to reassure the nation’s largest gathering of gun owners that he would be an aggressive defender of gun rights if elected president — and that President Obama would be the opposite if he wins a second term.

In an address to some of the 65,000 attendees of the annual meeting of the National Rifle Association, Romney pitched himself as a staunch defender of constitutional rights, including the right to bear arms.

But as he works to quickly pivot from a primary spent wooing conservatives to a general-election battle for independent votes, Romney spent most of the speech talking more broadly about economic and religious freedoms, using constitutional language that would appeal to NRA supporters to address a wider range of issues.

“This president is moving us away from our Founders’ vision. Instead of limited government, he is leading us toward limited freedom and limited opportunity,” Romney said. “As president, the Constitution would be my guide, and the Declaration of Independence my compass.”

Romney’s address to the yearly gathering came just three days after former U.S. senator Rick Santorum (Pa.) suspended his campaign, likely sealing the Republican nomination for Romney.

According to Romney’s campaign, the NRA speech was the first of a series of general-election addresses that the former governor will make to attempt to crystallize the choice between him and Obama on issues of fundamental freedoms. Romney spoke about expanding the economy by reducing regulations and taxes, and he accused Obama of infringing on religious liberties.

He referred to “freedom” 29 times in the speech and used the word “gun” just once. But he offered a robust defense of gun rights.

“We need a president who will enforce current laws, not create new ones that only serve to burden lawful gun owners. President Obama has not; I will,” he told thousands of NRA members, speaking on the floor of the domed stadium that is home to the St. Louis Rams. “We need a president who will stand up for the rights of hunters, and sportsmen, and those seeking to protect their homes and their families. President Obama has not; I will.”

White House spokesman Jay Carney told reporters Friday that Obama is focused on “common-sense actions that protect the Second Amendment rights of Americans while ensuring that those who should not have guns under existing law do not get guns.”

Former House speaker Newt Gingrich, who remains in the GOP race, also addressed the convention, as did Santorum.

Some gun owners remain skeptical about Romney, who once promised while running for Massachusetts governor in 2002 not to “chip away” at the state’s restrictive gun laws. “I believe they help protect us and provide for our safety,” he said then.

In an op-ed in Politico on Friday, former Ohio governor Ted Strickland (D) accused Romney of having a gun record “more scattered than buckshot pellets.”

“Romney is hardly a consistent Second Amendment defender, or a lifelong sportsman, or a longtime gun owner. But that’s not the worst part. The worst part is that he pretends to be all these things — pandering shamelessly to voters just as he does on every issue under the sun,” wrote Strickland, who is a co-chair of the Obama campaign.

But Romney has taken pains this year to shore up his conservative position on gun rights. At a January debate in South Carolina, Romney said he enjoyed hunting and would oppose new efforts at gun control.

“I do not believe in new laws restricting gun ownership and gun use,” he said.

Romney’s campaign has said he owns two shotguns, although he has been vague about when he bought them and how often he uses them.

He received a standing ovation with muted applause as he took the stage Friday, but the crowd seemed to warm to him as he spoke.

Romney offered a broad critique of Obama’s “assault on our freedoms — our economic freedom, our religious freedom and our personal freedom” — pivoting from the gun issue to taxes and other concerns.

While Obama has not made gun control a priority in his first term, Romney accused the president of preparing to remake the Supreme Court with justices who could be unfriendly to gun rights, citing a comment caught by a hot microphone from Obama to Russian President Dmitry Medvedev last month that he will have “more flexibility” to deal with missile defense after the election.

“I’m not exactly sure what he meant by that, but looking at his first three years, I have a very good idea,” Romney said.

Before he began speaking, Romney brought wife, Ann, to the stage, telling the crowd, “I happen to think that all moms are working moms. And if you have five sons, your work is never over.”

The comments were his first about the dust-up over a Democratic operative’s remark that Ann Romney had “not worked a day in her life.” The crowd applauded heartily.

At the convention, where attendees were handed NRA buttons that read “All In,” as they entered the stadium floor, some gun owners said they remain skeptical about Romney’s commitment to the Second Amendment.

“I have to say, I’m a little bit worried about him,” said Stormy Hyatt, 70, a retired trucker from Wapello, Iowa, who had been supporting Santorum. He said a rousing speech can help but could not assuage all of his concerns. “I really only believe half of what I hear,” he said.