Some of them watched from the spectator galleries above the Senate floor. "Shame on you," shouted one, Patricia Maisch, who was present two years ago when a gunman in Tucson, Ariz., killed six and wounded 13 others, including former Rep. Gabrielle Giffords.
Vice President Joe Biden gaveled the Senate back into order after the breach of decorum.
Gun control advocates, including Obama, had voiced high hopes for significant action after the Newtown shootings. But the lineup of possible legislation gradually dwindled to a focus on background checks, and in the end even that could not win Senate passage. Chances in the Republican-controlled House had seemed even slimmer.
By agreement of Senate leaders, a 60-vote majority was required for approval of any of the provisions brought to a vote.
The vote on the background check was 54-46, well short of the 60 votes needed to advance. Forty-one Republicans and five Democrats voted to reject the plan.
The proposed ban on assault weapons commanded 40 votes; the bid to block sales of high capacity ammunition clips drew 46.
The NRA-backed proposal on concealed carry permits got 57.
In the hours before the key vote on background checks, Sen. Joe Manchin, D-W.Va., bluntly accused the National Rifle Association of making false claims about the expansion of background checks that he and Sen. Pat Toomey, R-Pa., were backing.
"Where I come from in West Virginia, I don't know how to put the words any plainer than this: That is a lie. That is simply a lie," he said, accusing the organization of telling its supporters that friends, neighbors and some family members would need federal permission to transfer ownership of firearms to one another.
The NRA did not respond immediately to the charge, but issued a statement after the vote that restated the claim. The proposal "would have criminalized certain private transfers of firearms between honest citizens, requiring lifelong friends, neighbors and some family members to get federal government permission to exercise a fundamental right or face prosecution," said a statement from Chris Cox, a top lobbyist for the group.
Said Sen. Chuck Grassley, R-Iowa, "Expanded background checks would not have prevented Newtown. Criminals do not submit to background checks."
Even before the votes, the administration signaled the day's events would not be the last word on an issue that Democratic leaders shied away from for nearly two decades until Obama picked up on it after the Newtown shootings.
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.
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 Senators 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 seek to defeat them in 2014.
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 per cent of Americans support stricter gun laws, down from 58 per cent in January. In that recent survey, 38 percent said they want the laws to remain the same and 10 per cent 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.
Senator Rand Paul, 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.
