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, yet another Republican — Sen. Kelly Ayotte of New Hampshire — declared she would vote against the background check measure. Her announcement, along with opposition from other Republicans and some moderate Democrats, left supporters heading toward defeat unless they could turn votes around in the final hours, a near impossible task.

Rejection of the provision would mark a jarring setback for gun control advocates, who had hoped December’s slayings of 20 children and six aides at a Newtown, Conn., elementary school would sway Congress to curb firearms violence.

“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 Wednesday. 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.”

In a written statement, Ayotte said the background check expansion “would place unnecessary burdens on law-abiding gun owners and allow for potential overreach by the federal government into private gun sales.”

Perhaps helping explain Democrats’ problems, an AP-GfK poll this month showed that 49 percent of Americans support stricter gun laws. That was down from 58 percent who said so in January.

Just over half the public — 52 percent — expressed disapproval in the new survey of how President Barack Obama has handled gun laws. Weeks after the Newtown slayings, Obama made a call for 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 Wednesday that gun control was a legitimate issue to debate but he didn’t think victims and their families should be used “like props” to politicize a tragedy. Families of victims of Newtown and other mass shootings have been lobbying lawmakers and appearing 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.

In a climactic day, the Senate planned to hold eight other votes Wednesday besides the one on background checks, all of them amendments to a broad gun control measure.

They included Democratic proposals to ban assault weapons and high-capacity ammunition magazines, which are expected to lose; a Republican proposal requiring states to honor other states’ permits allowing concealed weapons, which faces a close vote; and a GOP substitute for the overall gun measure.

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, announced he would back the assault weapons ban, rejecting 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, who say it would allow more guns into states with stricter firearms laws.

The votes were coming a day after former Rep. Gabrielle Giffords, badly injured in a 2011 mass shooting in Tucson, Ariz., and her husband, Mark Kelly, tried galvanizing gun control support by visiting Capitol Hill and attending a private lunch with Democratic senators.

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.

Wednesday’s first vote was on an amendment by Toomey and Sen. Joe Manchin, D-W.Va., extending 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 — Mark Pryor of Arkansas and Mark Begich of Alaska.

If all 31 oppose the Manchin-Toomey measure — and that is not certain — opponents would need just 10 more votes to prevail.

So far, 11 of 16 Republicans who voted last week to let debate on the gun bill begin have said they will oppose Manchin-Toomey. That would give foes of expanded background checks 42 potential votes — one more than they need to win.

Still uncertain was support from some Democrats from GOP-heavy states, including Max Baucus of Montana, Mary Landrieu of Louisiana and Heidi Heitkamp of North Dakota. Baucus and Landrieu 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.

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 AP-GfK 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.

(AP)