WASHINGTON (AP) — A bipartisan effort to expand background checks was in deep trouble 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, so many Republicans had declared their opposition to the background check measure that supporters — mostly Democrats — seemed headed to defeat unless they could turn votes around in the final hours. Supporters seemed likely to lose some moderate Democratic senators as well.

“As we sit here this morning, we don’t have the votes,” Sen. Patrick Toomey, R-Pa., a sponsor of the background check compromise, told the National Review on Wednesday. “Now, there are enough undecided people that it’s still possible, but I’ll be the first to admit that there is a very, very narrow path” to victory.

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 — a month after the December killings of 20 children and six aides at a Newtown, Conn., elementary school propelled gun violence into a national issue.

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.