Biden's presence was a purely symbolic move since each proposal required a 60-vote majority to pass and he would not be called upon to break any ties. Democratic aides said in advance the issue would be brought back to the Senate in the future, giving gun control supporters more time to win over converts to change the outcome.
Obama, standing near Giffords and relatives of other shooting victims, said at the White House public opinion was strongly behind expanded background checks. Despite that, opponents of the legislation were "worried that the gun lobby would spend a lot of money" at the next election, he said.
"So all in all this was a pretty shameful day for Washington," he added.
Giffords, in a piece published late Wednesday on the New York Times' op-ed page, said she was "furious" that the Senate blocked the gun legislation. She accused senators who opposed new gun regulations of "cowardice," saying their decisions were "based on political fear and on cold calculations about the money of special interests like the National Rifle Association."
The day's key test concerned the background checks, designed to prevent criminals and the seriously mentally ill from purchasing firearms. Under current law, checks are required only when guns are purchased from federally licensed firearms dealers. The proposal by Manchin and Toomey called for extending the requirement to other sales at gun shows and on the Internet.
On the vote, Democratic Sens. Mark Begich of Alaska and Max Baucus of Montana joined Pryor and Heitkamp in voting against the proposal. Senate Majority Leader Harry Reid, a supporter of the plan, switched his vote to the prevailing "no" side to permit him to call for a revote in the future.
Begich, Pryor and Baucus are all seeking re-election next year. In an indication of the intensity of the feelings on the issue, the Progressive Change Campaign Committee, a liberal group, swiftly announced it would run ads contrasting their votes with polls showing overwhelming popular support for gun curbs.
Among Republicans, Sens. Susan Collins of Maine, Mark Kirk of Illinois, John McCain of Arizona and Toomey sided with Democrats.
Numerous polls in recent months have shown support for enhanced gun control measures, including background checks, though it may be weakening.
An Associated Press-GfK poll this month showed that 49 percent of Americans support stricter gun laws, down from 58 percent in January. In that recent survey, 38 percent said they want the laws to remain the same and 10 percent want them eased.
Obama has made enactment of greater curbs a priority on his domestic agenda in the months since the massacre at Newtown, making several trips outside Washington to try and build support. Last week, he traveled to Connecticut, and he invited several parents to fly back to Washington with him aboard Air Force One so they could personally lobby lawmakers.
To an unusual degree for professional politicians, some senators said afterward that they had not wanted to meet with the mothers and fathers of the dead, or said it was difficult to look at photographs that the parents carried of their young children, now dead.
Sen. Rand Paul, R-Ky., said before Wednesday's vote, "I think that in some cases, the president has used them as props, and that disappoints me."
Without referring to Paul by name, Obama rebutted him firmly. "Do we really think that thousands of families whose lives have been shattered by gun violence don't have a right to weigh in on this issue?" he said.
At the White House, press secretary Jay Carney said some of them had met earlier in the day with lawmakers, who he said should "consider who they're representing.
"Ninety percent of the American people support expanded background checks," he said.
The NRA told lawmakers it intended to keep track of how the votes were cast, and consider them in making decisions about its efforts in the midterm elections for Congress next year.
An opposing group, Mayors Against Illegal Guns, funded by New York City Mayor Michael Bloomberg, said it would do likewise.
The NRA has a long track record in electoral politics, and is viewed by lawmakers in both political parties as unusually effective. Bloomberg's organization has yet to be tested.
In the AP-GfK poll, among independents, support for stricter gun laws dipped from 60 percent in January to 40 percent now. About three-fourths of Democrats supported them then and now, while backing among Republicans for looser laws about doubled to 19 percent.
The survey was conducted from April 11-15 by GfK Roper Public Affairs and Corporate Communications. It involved landline and cellphone interviews with 1,004 randomly chosen adults and had a margin of sampling error of plus or minus 3.9 percentage points.
Associated Press writer Laurie Kellman, AP Director of Polling Jennifer Agiesta and news survey specialist Dennis Junius contributed to this story.
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