NEW YORK In the end, nothing could persuade enough U.S. senators to approve the most significant gun legislation in two decades:
Not the carnage from Newtown, Connecticut, where 20 children and six adults were massacred by a gunman in December, igniting a national debate on gun control.
Not the impassioned pleas of Newtown survivors' families, whose calls for expanded background checks for gun buyers so moved a pro-gun senator from West Virginia that he became their advocate.
And not the support of President Barack Obama, who was inspired by Newtown to make gun control the first major initiative of his second term.
The U.S. Senate's key vote on Wednesday wasn't exactly a rejection of expanded background checks, gun-control advocates were careful to point out.
Most senators - 54 - approved the measure, which polls indicated was backed by more than 80 percent of Americans. But because Republicans threatened to use a filibuster to block any gun proposal that did not get 60 votes in the 100-member Senate, the plan to expand background checks to sales made online and at gun shows fell short.
And just like that, the most aggressive push for gun control in a generation did, too.
How galling was the defeat for the new gun-control movement?
Another Senate vote on Wednesday told the story: Four months after Newtown jolted America, the 54 senators who voted to expand background checks were three less than the 57 who voted for a Republican-backed plan to expand Americans' rights to carry concealed weapons.
That tally also was short of the 60 votes needed to clear the Senate. But taken together, the votes made a statement about Americans' devotion to guns - there are estimated 270 million guns in circulation across the nation - and the success of the powerful gun lobby, led by the National Rifle Association.
So where do gun-control advocates go from here?
On Wednesday, amid their disappointment, frustration and anger, it was clear that the new groups who have driven the gun-control agenda since Newtown already were taking aim at the 2014 and 2016 elections.
New York City Mayor Michael Bloomberg, whose personal fortune has helped to fund a group called Mayors Against Illegal Guns, called Wednesday's vote a "damning indictment of the stranglehold that special interests have on Washington."
He said that his group would work to defeat opponents of gun control in the 2014 midterm elections, saying that "our ever-expanding coalition of supporters will work to make sure that voters don't forget."
GIFFORDS: 'I WILL NOT REST'
In an opinion piece that was to appear in The New York Times on Thursday, former U.S. Representative Gabrielle Giffords - who was critically wounded in a mass shooting in Tucson, Arizona in 2011 and founded Americans for Responsible Solutions, a group that focuses on gun violence - vowed not to give up.
"On Wednesday, a minority of senators gave in to fear and blocked common-sense legislation that would have made it harder for criminals and people with dangerous mental issues to get hold of deadly firearms," Giffords wrote.
"I will not rest until we have righted the wrong these senators have done," she continued. "... I am asking every reasonable American to help me tell the truth about the cowardice these senators demonstrated. ... I'm asking citizens to go to their offices and say, 'You've disappointed me, and there will be consequences.' "
At the White House, an angry Obama struck a similar tone.
"This was a pretty shameful day for Washington," he said. "This effort is not over. ... If this Congress refuses to listen to the American people and pass common-sense gun legislation, then the real impact is going to have to come from the voters."
'THEY WILL HAVE A LONG MEMORY'
For all the determination of the gun-control groups - and for all of the public support they enjoy - the Senate's vote showed that challenging the nation's attachment to guns or Americans' devotion to guns is a politically tenuous exercise.
Affection for guns and hunting - and respect for the NRA, which spent $18.6 million in the 2012 campaign cycle, according to the Sunlight Foundation - was a theme throughout Wednesday's debate.
Several senators - including West Virginia Democrat Joe Manchin, who co-sponsored the background checks plan and often became emotional in praising the Newtown families - made a point of saying that they supported gun rights and had been proud to be in line with the NRA's pro-gun platform.
Four Republicans - Mark Kirk of Illinois, Susan Collins of Maine, John McCain of Arizona and Pat Toomey of Pennsylvania, Manchin's co-sponsor - backed the background checks plan.
But four Democrats from gun-friendly states - Max Baucus of Montana, Mark Begich of Alaska, Heidi Heitkamp of North Dakota and Mark Pryor of Arkansas - rejected the background checks plan. Baucus, Begich and Pryor are up for re-election in 2014.
Some gun-control advocates predicted that the issue could become a leading concern in the 2016 presidential campaign.
"Voters will wake up in the morning to find that Senate hasn't passed background checks. They will have a long memory," said Josh Horwitz, executive director of the Coalition to Stop Gun Violence, a collection of 47 national organizations.
Horwitz said Republican senators in politically divided states such as New Hampshire, Ohio and North Carolina could see themselves at risk if they oppose more background checks.
"Mayor Bloomberg has the wherewithal to match NRA resources, which is a completely new phenomenon in the gun debate," said Matt Bennett of Third Way, a centrist Democratic organization that has been active in the gun debate.
Last month Bloomberg footed the bill for a $12 million ad campaign, which ran in 13 states and was aimed at pressuring lawmakers to support expanded background checks.
GUN RIGHTS GET A BOOST
Gun-rights advocates acknowledge they have competition that is perhaps unprecedented, but they note that Bloomberg's millions didn't lead to Senate passage of the background checks plan. They note that while Newtown inspired the gun-control movement, it also boosted the NRA and its supporters.
Sales of guns and ammunition soared, fueled in part by fears that Obama's gun-control package would make both scarce. Stock prices of gun makers such as Smith & Wesson Holding Corp and Sturm, Ruger & Co dipped after Newtown, but now are near where they were before the shootings.
And although there has been a wave of new gun-control laws in states led by Democrats, several states led by Republicans have eased gun restrictions in the months since Newtown.
In a statement the NRA praised the Senate's action, saying that the measure would have "criminalized certain private transfers of firearms between honest citizens."
Some gun-control advocates said they feared that they had seen their best chance for change in 20 years pass. Others said they worried it would come again soon.
"I wish Newtown was our last mass shooting," said Daniel Webster, director of the Johns Hopkins Center for Gun Policy and Research. "There are going to be more mass shootings. There are going to be more incidents where people will try to figure out what in the hell is wrong here."
(This version of the story corrects the senator's name to Mark Kirk from Ron Kirk in paragraph 23.)
(Additional reporting by Edith Honan; Editing by David Lindsey and Lisa Shumaker)