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WASHINGTON - Unveiling a sweeping new gun control agenda driven by the deaths of 20 children in the Sandy Hook school massacre, President Obama said members of Congress are "going to have to have a debate, and examine their conscience."

Nowhere will that examination be more searching than in outstate Minnesota, where support for gun rights is strong and Democrats control all three big rural districts.

This checkerboard of farms, forests and prairie could well be the firewall that determines how far the administration can push a bitterly divided Congress to act on an expansive overhaul of gun laws.

Amid peaking emotions and stiffening gun lobby opposition, one centrist Minnesota Democrat has already altered course, while others find themselves having to finesse or refine their public postures on politically touchy measures that have long been stymied by a wary Congress.

"I've got to live with myself on these things," said Tim Walz, a southern Minnesota Democrat who runs with an "A" rating from the National Rifle Association (NRA). "There's a point where I've got to say, how do I want to wake up tomorrow?"

Walz has softened his long-held opposition to banning military-style assault weapons, one of the central planks of Obama's gun-control plan, along with universal background checks and limits on high-capacity ammunition clips.

But Walz isn't all the way there. "I have a responsibility as someone who understands firearms to explain what a semi-automatic weapon is," he said. "That can include my Benelli shotgun for duck hunting. It's a semi-automatic that can shoot one bullet after another by pulling the trigger."

'Devil in the details'

Walz isn't the only one straddling the divide between staunch defenders of the Second Amendment right to bear arms and those who decry the proliferation of guns in America as a threat to public safety.

Even more entrenched in the NRA firmament is Democrat Rep. Collin Peterson, who prides himself as one of the top marksmen in Congress and partly blames the last assault weapons ban in 1994 for the Democrats' loss of the U.S. House that year.

Peterson notes that Democrats have stayed pretty much at arms-length from the gun control agenda since then. But the shootings in Newtown, Conn., might have changed all that -- possibly to the peril of Democrats in rural districts like his.

Peterson remains skeptical of an assault weapon ban and other ideas that he says "have been tried before." But in the wake of Newtown, he's keeping his options open. "The devil is always in the details, so I'm going to keep an open mind and not make any decisions until I've seen specific legislative language."

'Assault weapon to shoot a duck'

More outspoken in his support for the president's plan is newly elected Democrat Rick Nolan, who beat incumbent Chip Cravaack in northern Minnesota despite the direct intervention of NRA President David Keene, who stumped for the Republican in the closing days of the campaign.

While emphasizing his support for gun rights, Nolan, a lifelong hunter, recently tweeted, "I don't need an assault weapon to shoot a duck."

One thing all three rural Democrats have in common is that the National Republican Congressional Committee has put them on a list of top takeover targets in 2014.

While much has been made of the public outrage over the carnage in Newtown and other recent mass shootings, a sense of alarm also has grown among gun rights advocates.

"What's going on now has really gotten people excited out here," said Cedric Scofield, legislative committee chairman of the NRA-affiliated Minnesota Shooting Sports Association. "It's never been this hectic."

Franken: 'In principle'

Republicans, who have generally condemned Obama's agenda as violating the Second Amendment, also see an opening against Sen. Al Franken, D-Minn., who is up for statewide re-election next year.

Few on Capitol Hill have had to work harder to bridge the divide in recent days than Franken, whose initial statement on the Obama plan made no mention of his support for an assault weapon ban.

After news reports emerged Thursday suggesting he was undecided, Franken issued a new statement, saying he supports an assault weapon ban "in principle."

Republican National Committee spokesman Ryan Mahoney accused him of "running away from his past support of widespread gun bans."

As Franken did when elected to the Senate in 2008 with an "F" rating from the NRA, he emphasized his support for the right to "own firearms for collection, protection and sport."

But before the crossfire over Obama's plan, Franken, along with Walz and Nolan, had been focusing his attention on the link between violence and lack of access to mental health treatment, something Franken lobbied to get into the administration plan.

Gun control advocates recognize that in the face of near-universal GOP opposition, much of Obama's plan will depend on the political realities facing Democrats in regions with strong hunting traditions like Minnesota.

"There's no question, it's easier for some than others," said Minneapolis Mayor R.T. Rybak, who attended last Wednesday's White House ceremony rolling out the president's gun agenda for Congress. "I'm from a big city in a rural state, and our challenge is to balance these issues together."

But Protect Minnesota chief Heather Martens, who met with Vice President Joe Biden's gun violence task force this month, said rural Democrats aren't the only ones who should be feeling the heat.

Martens said suburban Minnesota Republicans like John Kline and Erik Paulsen should also be minding the new political terrain since Newtown. "Their constituency very strongly supports gun violence prevention like background checks," she said. "That should be a slam-dunk in their districts."

'That's fear'

With polls showing nearly 60 percent of Americans supporting a ban on assault weapons, Martens and other gun-control advocates believe the NRA's hold on Congress has been weakened.

"There's this banter in Congress that some have a fear of the gun lobby," said Chaska Police Chief Scott Knight, who appeared before a special congressional panel last week. "That might cause them some discomfort. It might cause them some heartburn. That's not fear. Fear is what went through the hearts and minds of those 20 children in Connecticut."

Hamline University law professor Joe Olson, who heads the Minnesota Gun Owners Civil Rights Alliance, believes that reports of the NRA's demise have been greatly exaggerated.

"The NRA doesn't have the power to get people elected," he said, "but it does have the power to get people un-elected."

To Walz, who says he's not abandoning his core NRA principles of lawful gun ownership, the group's influence remains an uncertain factor in his political fortunes.

"If people think your votes are being influenced by outside groups," Walz said, "they probably have a very low opinion of you anyway."

Kevin Diaz is a correspondent in the Star Tribune Washington Bureau.