WASHINGTON — A bipartisan effort to expand background checks faced almost certain defeat Wednesday as the Senate approached a long-awaited vote on the linchpin of the drive to curb gun violence.
As the showdown drew near, an Associated Press-GfK poll showed ebbing public support for tightening gun control laws.
With the roll call just hours away, three more senators — Republican Kelly Ayotte of New Hampshire and Democrats Heidi Heitkamp of North Dakota and Mark Pryor of Arkansas — said they opposed the background check measure.
Their announcements, along with opposition from other Republicans and moderate Democrats, left supporters heading toward defeat unless they could turn votes around in the final hours, a near impossible task.
Rejection of the proposal would be a jarring setback for gun control advocates, who hoped the Dec. 14 shooting rampage that killed 20 children and six adults at a Newtown, Conn., elementary school would sway Congress to enact new firearms restrictions.
Defeating the background check plan also would give a victory to the National Rifle Association, which has fought the idea as a misguided crackdown on gun rights that criminals would ignore anyway.
"As of this morning, we're short. We need more votes. It's close," Sen. Joe Manchin, D-W.Va., a sponsor of the background check compromise, said in a brief interview. Asked how he could get the needed votes with so many opponents, he said, "We're just hoping the good Lord will enter their heart and maybe change a few."
The White House said it wasn't giving up hope. Presidential spokesman Jay Carney said President Barack Obama was working on building support.
Perhaps helping explain Democrats' problems, an AP-GfK poll this month showed that 49 percent of those surveyed support stricter gun laws. That was down from 58 percent in January.
By comparison, 52 percent expressed disapproval in the new survey of how Obama has handled gun laws. Weeks after the Newtown slayings, Obama made near-universal background checks the heart of his gun control plan.
"Every once and awhile we are confronted with an issue that should transcend politics," Obama said in an interview that aired Wednesday on NBC's "Today" show. "And now's the time for us to take some measure of action that's going to prevent some of these tragedies from happening again."
Sen. Rand Paul, R-Ky., said gun control was a legitimate issue to debate but didn't think victims and their families should be used "like props" to politicize a tragedy.
Relatives of victims of Newtown and other mass shootings have lobbied lawmakers to restrict guns, and several planned to be in the visitors' gallery during Wednesday's vote. Many have appeared at news conferences, including at the White House.
"I think that, in some cases, the president has used them as props and that disappoints me," Paul said at a breakfast sponsored by The Christian Science Monitor.
Carney responded that the Newtown families were in Washington "because their children were murdered. They're here asking the Senate to do something that's common sense."
The Senate planned eight other votes in addition to one on background checks. Each is an amendment to a broad gun control measure.
They included Democratic proposals to ban assault weapons and high-capacity ammunition magazines; the two were expected to lose. There also was a Republican proposal requiring states to honor other states' permits allowing concealed weapons; that was facing a close vote.
As the day's debate began, Senate Minority Leader Mitch McConnell, R-Ky., set the tone for the GOP, whose members have largely opposed many of the Democratic proposals.
"The government shouldn't punish or harass law-abiding citizens in the exercise of their Second Amendment rights," he said.
Senate Majority Leader Harry Reid, D-Nev., who has backed some gun rights efforts in the past, said he would back the assault weapons ban. He rejected some opponents' claims that confiscating weapons would leave them vulnerable to an out-of-control government.
"I'll vote for the ban because maintaining law and order is more important than satisfying conspiracy theorists who believe in black helicopters," he said.
The concealed weapons amendment, seen by advocates as protecting gun rights, was vehemently opposed by gun control groups, which say it would allow more guns into states with stricter firearms laws.
Background checks, aimed at screening out criminals and the seriously mentally ill from getting firearms, now apply only to purchases handled by licensed firearms dealers.
The amendment by Manchin and Sen. Patrick Toomey, R-Pa., would extend the checks to firearms sales at gun shows and online. The compromise was widely seen as advocates' best chance for winning enough GOP votes to muscle broadened checks through the Senate.
Opponents will need just 41 of the Senate's 100 votes to derail the Manchin-Toomey background check plan.
Thirty-one senators voted last week to completely block debate on overall gun legislation. Just two were Democrats — Pryor and Mark Begich of Alaska.
If all 31 oppose the Manchin-Toomey measure, and that was not certain, opponents would need just 10 more votes to prevail.
So far, 12 of 16 Republicans who voted last week to let debate on the gun bill begin have said they would oppose Manchin-Toomey. That would give foes of expanded background checks 42 potential votes, or one more than they need to win.
Still uncertain was support from some Democrats from GOP-heavy states, including Max Baucus of Montana and Mary Landrieu of Louisiana. Both face re-election next year.
The Senate gun bill would extend background checks to nearly all gun purchases, toughen penalties against illegal gun trafficking and add small sums to school safety programs.
The AP-GfK poll found that overall, 49 percent said gun laws should be made stricter while 38 percent said they should stay the same.
The poll 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.