Washington — Even gun control supporters knew congressional approval of new gun restrictions would be difficult, but their stunning defeat in the Senate this week prompted new looks at the gun lobby’s relationship with Washington lawmakers.

“I was astonished,” said Sen. Richard Blumenthal, D-Conn., of the failure to secure 60 votes in the Senate to approve expanded background checks of gun buyers.

Blumenthal said he misjudged the strength of the gun lobby. He said he spent hours lobbying swing votes on the Republican and Democratic sides of the aisle and was surprised the effort fell short.

“Phone calls from constituents and emails [opposing gun control] had an effect,” he said. “Special interests like the National Rifle Association have a deeply entrenched stronghold that spans more than a generation.”

Gun violence victims were also stunned by the Senate vote.

“I have no idea what happened,” said Roxanna Green, mother of 9-year-old Tucson, Ariz., shooting victim Christina Green. “It was common-sense regulation designed to save lives.”

The NRA used traditional methods to ward off gun control proposals born of the tragic shootings in Newtown.

It galvanized its members with its trademark orange postcards and threatened lawmakers who voted against them with a poor NRA ratings opponents could use against them. The NRA also ran some ads.

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One, posted on political news websites Wednesday, the day of the Senate vote, said the nation’s police officers overwhelmingly oppose President Obama’s gun control agenda.

“President Obama and [New York City] Mayor Bloomberg are pushing gun control,” a narrator says. “But America’s police say they’re wrong.”

Not only did the proposal to expand FBI background checks fail, but amendments that would have reinstated an assault weapons and high-capacity magazine ban were defeated by even wider margins.

Meanwhile, several NRA-backed proposals, including one that would greatly expand gun rights by allowing people who have concealed weapons permits to carry their guns nationwide, received far greater support. The concealed carry provision won 57 votes, just three shy of the 60-vote threshold. But some say the NRA’s clout is not the reason for the failure of the gun-control bill.

“The first thing to remember and emphasize is that the routinization of the filibuster has created a 60 vote supermajority hurdle in the Senate that is a new way of doing — or rather not doing — business,” said Thomas Mann, senior fellow at the Brookings Institution.

Having received 54 votes, had  a simple majority of votes been needed, the gun control provision would have been approved.

Tribal behavior

Mann also said the “contemporary Republican Party” was also a factor.

“This is the same partisan opposition that has killed, weakened, or discredited many of President Obama’s proposals,” he said. “Republican opposition is tribal and strategic, and it is very hard for individual senators to defect from the party line.”

Also there’s a special relationship between Republican interest groups, with the NRA being among the most visible, and the GOP that has made those groups part of the “Republican party network,” Mann said.

“The intensity of the leaders, funders and activists in this network is very hard to overcome,” he said. “But I suspect this may be their high point — an attentive and engaged public can eventually, and I believe will, get the last word.”

In the wake of the resounding defeat of Obama’s gun control agenda, advocates hope public furor will counter the forces that prevented senators from voting for gun control. They want the bill to have another chance, maybe even in this Congress.

Senate Majority Leader Harry Reid hasn’t explained why he brought up the gun legislation before there were enough votes to approve it.

On Thursday, he suspended debate on gun legislation indefinitely.

“I’ve spoken with the president,” Reid said. “He and I agree that the best way to keep working towards passing a background check bill is to hit a pause button and freeze the background check bill where it is…this will allow senators to keep negotiating.”

Family members of Sandy Hook Elementary School victims and others affected by gun violence are not ready to give up the fight.

“I didn’t ever think this would happen overnight,” said Neil Heslin, father of Jesse, a 7-year-old  Newtown victim.

Heslin has been testifying in favor of gun control and lobbying lawmakers for months, often carrying a large framed photo of his son to congressional offices. On Wednesday, he stood on the podium with Obama, who blamed Republicans for the defeat of gun control.

Doug Thornell, senior vice president of SKDKnickerbocker, the political consulting firm that produced ads for Mayors Against Illegal Guns said in the aftermath of the vote, said, “all you can do is try to move public opinion on your side.”

On Thursday Mayors Against Illegal Guns held a press conference in Florida to condemn Sen. Marco Rubio, R-Fla., for his part in blocking the gun legislation, creating the need for 60 votes to pass it.

But some who voted for gun control may also feel the heat.

Fallout from the gun control vote may impact next year’s Senate elections, said Jennifer Duffy, senior analyst at the Cook Political Report.

Sens. Mary Landrieu, D-La., and Kay Hagan, D-N.C., are two vulnerable Democrats who voted for the background check provision.

“They come from pretty pro-gun states,” Duffy said. “If nothing else, their votes will ratchet up the intensity of Republicans and their desire to see them defeated.”

Landrieu and Hagan represent largely rural states where gun ownership is an important part of local culture. But as the nation’s rural areas shrink and suburbs grow, the NRA’s influence is expected to wane. That’s what is happening in Pennsylvania, where Republican Sen. Patrick Toomey, was pressured to negotiate with Democrats on background checks.

Blumenthal accused the NRA of disinformation and deception that “engendered fears.” But he also said, “the NRA’s days of blocking progress are very, very limited.”