WASHINGTON - Four months ago, President Barack Obama promised a grieving nation he would do everything in his power to change gun laws after 26 students and staff were shot to death at Sandy Hook Elementary School. Turns out his power and the impassioned pleas of devastated families were no match for the force of gun rights advocates in Congress and across the nation.

The National Rifle Association and its energized supporters overcame national outrage over the deaths of innocent first-graders. The Senate rejected expanded background checks for gun buyers in the face of strong public support for the change, pleas from a former congresswoman still healing from bullet wounds and a campaign bankrolled by a billionaire mayor. Foes of new controls were stronger than Obama's moral indignation from the president's "bully pulpit" and his political machine that won two elections but couldn't translate its grass-roots power to win the gun vote.

Obama, angry and defiant over the defeat, is vowing to fight on. And the NRA says it is taking him seriously. "We are prepared for a very long war and a very expensive war," association spokesman Andrew Arulanandam said Thursday.

The NRA's success is built on the passion of gun advocates, activists on both sides of the debate agree. That's how they were able to defeat expanded background checks despite polling that shows up to 90 percent of Americans support the idea.

"You know what I hear from the members of Congress?" said Vice President Joe Biden. "I just met with one. He says, 'Well that may be true, Joe, but that 10 percent who doesn't agree, they are going to show up. They're going to show up and vote. And that 90 percent thinks it's a good idea, but they're not going to vote for me or against me because of how I vote on this.'"

Arulanandam said he refers to NRA members as "super volunteers" who work on political campaigns and get to know lawmakers personally so their voices are even more powerful in the debate. A Washington Post-ABC News poll taken last week shows they are more likely to speak up: 20 percent of gun owners and 14 percent of people who live with a gun owner said they contacted a public official on gun control, compared to 10 percent of adults with no gun in their home.

The changes at the heart of the gun control bill failed to get the 60 votes needed in the Senate on Wednesday. On the background-checks issue, four Democrats voted against it. They all come from states Obama lost last year. Three of the four face tough re-election fights next year.

Arulanandam rejected Obama's contention that a wide majority of NRA households actually supported the defeated legislation. "Then who was lighting up phone lines and going to town hall meetings?" he asked.

The background-check proposal was co-authored by Sen. Joe Manchin, D-W.Va., who won re-election after running an ad in which he fired a rifle and boasted of his NRA endorsement. At a breakfast sponsored by The Wall Street Journal, he predicted the legislation backed by Obama would have passed easily if the NRA hadn't threatened to use senators' votes to determine whom it would support in next year's midterm elections.

Manchin also said background checks would have been approved if the Senate had moved more quickly, when the nation's heartache over the Newtown, Conn., school shootings was still in focus. A recent Associated Press-GfK poll found that 49 percent of Americans back stricter gun laws, but that's down from 58 percent in January.

"If we'd have gone to a bill like this immediately, boom," Manchin said at the breakfast, predicting it would have gotten 65 to 70 votes. "You seize the moment."

Manchin also blamed a broader liberal agenda in Washington with making passage difficult. He said lawmakers shifting their positions on gay rights and immigration found it hard to also vote for gun control. He said constituents would ask lawmakers who made all those changes, "Are you still the same person that we sent?"

The NRA also benefits from electoral dynamics, with a group of moderate Democrats facing re-election in rural states, where residents are far more likely to live in a home with a gun. The AP-GfK poll found most urban and suburban residents - 56 percent and 52 percent, respectively - say gun laws should be made more strict, compared with 41 percent of rural residents.

Congressional officials said that in the run-up to Wednesday's vote, the bill's supporters tried to gain backing for expanded background checks by creating an exemption for sales that occurred in remote areas, possibly 50 miles from the nearest federally licensed gun store. The aim was to win the votes of Democratic holdouts Mark Begich of Alaska and Heidi Heitkamp of North Dakota and at least one Republican, but in the end, the effort failed.

Senate Majority Leader Harry Reid on Thursday pulled the bill before a final vote and said he would bring it back again after gun control activists have more time to make their voices heard.

"I've spoken with the president. He and I agree that the best way to keep working toward passing a background-check bill is to hit a pause and freeze the background-check bill where it is," Reid said.

Gun control supporters say they hope the defeat will energize their more-silent majority to become an increasingly powerful counterpoint to the NRA. Dan Gross, president of the Brady Campaign to Prevent Gun Violence, said chairwoman Sarah Brady reminded him after the vote that "sometimes it takes a good defeat."

She would know. After her husband, former White House press secretary Jim Brady, was partially paralyzed in the shooting of President Ronald Reagan, it took repeated tries over six years to pass a bill named after him that instituted background checks.

"We have to prove to them that this is an issue about which the overwhelming majority of the public agrees and is passionate enough to hold them accountable," Gross said in an interview. "We have to prove to them it's safe to do the right thing, and unsafe for them to do the wrong thing."

New York City Mayor Michael Bloomberg, a media executive who has financed ads aimed at electing lawmakers who support gun control, said Thursday he would work to defeat senators who voted against background checks. A fundraising email to fund a similar effort went out from Americans For Responsible Solutions, the group founded by injured former Rep. Gabrielle Giffords, D-Ariz., and her husband, Mark Kelly.

Asked which senators would be targeted for their opposition, Kelly, a former astronaut and Navy pilot said: "It's a target-rich environment, as we would say in the military."

The families of some of the Sandy Hook victims came as late entrants attempting to counter the influence of gun-rights activists on the debate. Over five days in Washington during the past two weeks, they met with 35 senators to ask for their support in memory of their children. They were credited with helping stop a block of debate on the bill, but even their emotional pleas were not enough to win passage.

Some say they, too, won't give up.

This week, for gun control advocates nurturing fading hopes of Senate passage of expanded background checks, the breaking point came Tuesday and early Wednesday, when a pair of GOP senators announced they'd oppose the effort.

Gun control supporters believed that Republican Sens. Dean Heller of Nevada and Kelly Ayotte of New Hampshire were still possible votes for the measure. But Heller said Tuesday he'd oppose the compromise - which had been worked out by Manchin and Pennsylvania Republican Pat Toomey - and Ayotte said the same Wednesday morning.

They would have been the 56th and 57th votes. Had they agreed, gun control supporters say they might have had a chance to persuade three of the four Democratic senators who ended up voting "no" to instead push the measure over the top by getting to the needed 60 votes,