WARREN, N.H. — The contentious political fight over gun control moved into the White Mountains of New Hampshire on Tuesday as gun-control activists began to focus on Sen. Kelly Ayotte (R-N.H.) as a prime target in their effort to revive their push for stricter gun laws.

Ayotte was a key, high-profile vote against the bipartisan plan to expand the national gun ­background-check program, which failed in the Senate two weeks ago despite overwhelming public support and extensive efforts by the White House. The failure was widely seen as a triumph for the National Rifle Association.

Back home this week for a series of town hall meetings, Ayotte is facing new constituent anger and a coordinated effort by gun-control groups to turn her vote into a political liability. These organizations include Mayors Against Illegal Guns, the group founded by New York Mayor Michael R. Bloomberg (I), and the liberal think tank the Center for American Progress. Other groups are deploying organizers to New Hampshire, Arizona, Arkansas, Nevada and North Dakota in hopes of shaming moderate senators of both parties who voted against the background-check plan.

In New Hampshire, the national organizations are partnering with local groups that plan to follow her across the state.

“As simple as a background check is, it’s not burdensome,” said Karen Fester, 62, of Bath, N.H., a retired postal worker and member of a local gun club. “It’s just that the people who own gun shops or run gun shows don’t want their way of life threatened.”

Sen. Kelly Ayotte (R-N.H.) speaks at the Conservative Political Action Conference (CPAC) in National Harbor, Md., on March 15. (NICHOLAS KAMM/AFP/GETTY IMAGES)

Fester showed up in hopes of putting pressure on her senator even though she doesn’t expect Ayotte to change her mind. But by showing up, “it might make her pick up the phone or respond to my e-mails,” she said.

Judy Stadtman, co-founder of the Project for Safer Communities NH and a longtime liberal activist, said, “I have worked on a lot of issue campaigns in this state, and I’ve never seen this level of natural momentum on any issue.”

“There’s a sense that the people who support background checks know that they’re in the mainstream,” Stadtman said. “To be rejected by Ayotte like that, when it was so obvious that many of her constituents wanted her to vote for it — it was a tipping point.”

State Rep. Steve Shurtleff (D) gave Ayotte credit for facing her detractors at several scheduled town halls this week but said he thinks the senator will have to answer to voters on the background check vote, even if her re-election is still more than three years away. With his advancing age, he said, “I forget things a little more often. One thing I will remember in 2016 is Senator Ayotte’s vote on this very important legislation. Especially in the wake of the terrible tragedy we saw at Sandy Hook.”

Ayotte was the only senator from the Northeast to vote no on the measure, which emerged as the latest barometer of the ideological and partisan divide that has gripped Washington in recent years. Even in New Hampshire, where there is a long tradition of support for gun rights, one poll this year showed that almost 95 percent of New Hampshire residents support background checks. “Almost nine in ten (88%) of New Hampshire adults strongly favor this proposal, 6% favor it somewhat, and only 5% oppose it. Even 83% of gun owners favor this proposal,” according to a WMUR Granite State Poll conducted in February.

That has made the New Hampshire freshman an easy target for the gun-control groups as they seek to regroup after the loss on background checks in the Senate. As she travels the state, Ayotte has been confronted by signs that read, “We are the 90%!”

At her first town hall meeting in Warren on Tuesday, Ayotte delivered a lengthy PowerPoint presentation of her positions on gun control, sequestration, the federal deficit and implementation of the new health-care law. Then she asked a moderator to call on members of the audience who had submitted question topics in advance.

Some objected to the format, but eventually Ayotte called on Erica Lafferty, whose mother, Dawn Lafferty Hochsprung, was the principal of Sandy Hook Elementary School and a victim of the mass shooting in December. Lafferty had driven four hours from Connecticut to confront Ayotte.

Speaking to the senator, Lafferty recalled a meeting in Ayotte’s Washington office the day after she voted against the background-check plan.

“You had mentioned that day the burden on the owners of gun stores that the expanded ­background checks would cause,” Lafferty said. “I’m just wondering why the burden of my mother being gunned down in the halls of her elementary school isn’t as important?”

Her voice strained by a cold, Ayotte quietly explained that she voted against the plan because it was flawed and that it wouldn’t have stopped the Sandy Hook killer. She said she did not believe that it would have stemmed the flow of illegal guns or compelled the Justice Department to aggressively enforce or prosecute existing gun laws.

“What we need to do is focus on mental health, ultimately,” Ayotte said. “But I understand and respect that you have a different viewpoint.”“I took a lot of heat, I will say, from even members of my own party that didn’t like the fact that I voted to go to debate on this issue,” Ayotte added later. “We can have strong disagreements, but ultimately everything should be debated and discussed. And I’ll continue to do that.”

She argued that she had angered gun-control opponents by voting to allow the background checks measure to come to a vote in the first place.

Lafferty, whose parents used to vacation at a mountainside inn just a few towns away, said Ayotte’s answer on Tuesday was different than what she’s said before.

“I’m going wherever she goes next,” Lafferty said.

Ayotte, 44, was appointed New Hampshire attorney general in 2004 and reappointed twice by a Democratic governor. She survived a brutal three-way GOP Senate primary in 2010 and then trounced her Democratic opponent by 23 points in her first race for statewide office.

Once on Capitol Hill, she glided into the national spotlight as the Republican “amiga” challenging President Obama on national security alongside Sens. John McCain (R-Ariz.) and Lindsey O. Graham (R-S.C.).

Ayotte is the mother of two young children — and one of only four Republican women in the Senate, making her a coveted voice in the party. GOP presidential candidate Mitt Romney used her extensively as a surrogate on the campaign trail and reportedly considered her as a potential running mate.

But less than a year after flirting with national politics, she has infuriated many residents by voting against background checks.

The anger has boiled over onto the Granite State’s editorial pages, with several publishers marveling at the sharply worded critiques of Ayotte’s vote.

“In the name of terrorists and violent criminals, I would like to thank you for your vote protecting their rights to purchase guns without background checks,” a woman from Milford, N.H., wrote in a letter to the editor of the Cabinet Press newspaper. “After all, the gun manufacturers making billions on the incredible sales of guns and the N.R.A. leadership who profit from this must be protected at all cost,” added the woman, who concluded by saying: “Thanks, Kelly, sleep well.”

As she travels across New Hampshire, Ayotte need only to turn on the radio to hear some encouragement, as the NRA and the National Shooting Sports Foundation, a firearms industry trade association, began airing radio ads Monday to thank her. The NRA ad stars a female announcer who says that Ayotte “is not just a senator, she’s also a mom, who cares about protecting our kids.”

“She knows the only way to prevent tragedies like Sandy Hook is to fix our broken mental health system,” the announcer continues. “That’s why Kelly Ayotte brought Republicans and Democrats together on a bipartisan solution. And it’s why Kelly had the courage to oppose misguided gun-control laws that would not have prevented Sandy Hook.”

NRA spokesman Andrew Arula­nandam dismissed the increased activism on the other side.

“This is part of their larger game plan to try and manufacture support for their cause and to try to paint support for gun rights as a liability,” he said. “This is a fight that will be won on the ground, and that’s where the NRA is strongest. We’re able to mobilize people.”

Gun-control advocates think the failed Senate vote has been a mobilizing force on their side. Lisa Merrill of Meredith, N.H., said Tuesday was the first time she had attended a political event in her state. She felt compelled to show up at an Ayotte town hall later Tuesday in Tilton because her aunt was killed in a workplace shooting in Massachusetts a few years ago.

“I lost a loved one to gun violence, and I think if Senator Ayotte lost a loved one to gun violence she’d understand,” she said. Merrill doesn’t think Ayotte will change her mind on the gun issue, but by showing up Tuesday night, “I would hope that it would make her feel guilty and shame her,” she said.

In New Hampshire, the organizers are mostly younger, well-dressed 20-somethings wearing hipster sunglasses, presenting an odd juxtaposition at a town hall meeting packed mostly with retirees in flannel shirts and jeans.

Nancy Martlind, 64, of Sugar Hill, N.H., said she was not sure that her activism would change Ayotte’s opinion — but she sees a more immediate benefit.

“We have her on the record,” Martlind said of Ayotte. “Then there’ll be another big shooting incident and we’ll know where she stands.”

Ayotte’s popularity in New Hampshire may be on shaky ground. Her popularity stood at 50 percent in a Granite State Poll a week before the Senate vote. It is unclear whether her vote on background checks will affect those numbers.

At the town hall in Warren on Tuesday, the format of pre-selected question topics angered Eric Knuffke, 74, who stood up and asked to be heard after raising his hand failed to get him recognized.

The senator resisted. “I do every town hall meeting this way and have a process,” Ayotte told him.

“You like to regulate [the questions you take], but you don’t want to regulate guns?” he shouted. The room burst into applause.

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