Updated 8:33 p.m.

The push for stricter gun laws may return to the forefront of the congressional agenda in the coming weeks as at least two Republican senators who voted against a bipartisan proposal to expand the national gun background check system have approached Democrats about possibly restarting debate on the issue, according to senior Senate aides familiar with the talks

The issue of gun-control looked to be all-but abandoned after a resounding defeat in the Senate last month, but a new eagerness to engage on the issue comes after senators of both parties who voted against the background check proposal faced backlash in their home states from gun-control groups.

The aides, who asked not to be identified because they were not authorized to publicly discuss the talks, refused to identify the two Republicans.

But through spokespeople, Sens. Johnny Isakson (R-Ga.) and Jeff Flake (R-Ariz.), who voted to block the background check proposal, signaled they are open to a new debate if Democrats make significant changes to the plan.

Meanwhile, aides to Sen. Kelly Ayotte (R-N.H.), who voted against the background-check plan, disputed a new barrage of TV ads critical of her vote and said she remains opposed to the current bipartisan background check proposal.

Senate aides and activists pushing for stricter gun laws say there are likely two forthcoming windows of opportunity for the Senate to return to gun legislation: Either in late May after the consideration of an Internet taxation bill and a measure reauthorizing water resource development projects, or later in the summer, once senators willing to change their votes on the issue have had enough time to reconsider their position.

Reid noted that Ayotte faced strongly critical reactions from voters last week during a series of town hall meetings across her state. During those meetings, Ayotte said that she is willing to continue discussing the issue of gun-related violence, so long as legislative proposals include a plan to fix and bolster the nation's mental health programs.

Sen. Kelly Ayotte (R-N.H.). (AP)

"She's the only senator in the northeast to vote against background checks," Reid said of Ayotte, in the interview. "She went from a hugely positive number in New Hampshire -- her negatives now outweigh her positives. She is being hit every place she goes. So we are going to pick up some more votes. I may be able to get another Democrat or two. That would get us up to 57. We may only need three additional Republicans. So we'll see."

Keeping pressure on Ayotte, Mayors Against Illegal Guns, the gun-control group founded by New York Mayor Michael Bloomberg (I), released a new television advertisement in New Hampshire Monday attacking her for voting against the background check proposal. The ad stars several older voters and notes that 89 percent of Granite State voters supported the plan.

"Sen. Ayotte supports giving criminals a pass," one man in the ad says.

Ayotte spokesman Jeff Grappone called the new ads "completely false" and said that the senator voted for an alternative GOP plan to fix the background check system and strengthen mental health programs. As for Reid's comments, Grappone said the Senate leader "doesn’t speak for Senator Ayotte."

Another senator who voted against the plan, Jeff Flake (R-Ariz.), took to Facebook last week to acknowledge that his statewide approval ratings had taken a hit in part because of his vote on the background check proposal: ”Given the public’s dim view of Congress in general, that probably puts me somewhere just below pond scum," he said.

Flake spokesman Genevieve Rozansky said in an e-mail Monday that the senator "has said all along that background checks need to be strengthened, particularly with regard to the mentally ill.  So he is hopeful that changes will be made to Manchin-Toomey, or another proposal, that address his concerns regarding private sales, and that a bill will be brought back to the floor."

Lauren Culbertson, a spokeswoman for Sen. Johnny Isakson (R-Ga.), said the senator is open to further conversations about expanding background checks, but that the current proposal “would have to be significantly reworked” before he considered supporting the plan. Culbertson said that Isakson “has major concerns with its potential impact on private sales and on privacy issues.”

President Obama’s effort to overhaul the nation’s gun laws suffered a resounding defeat last month as supportive lawmakers fell several votes short of assuring final passage of the plan.

But conversations picked up again over the congressional recess, according to the aides, with Manchin once again taking the lead.

Manchin and Sen. Patrick J. Toomey (R-Pa.) brokered the deal that would have expanded the background check system to include most commercial firearms sales, but exempt private exchanges between family members and close friends.

Senators and their aides have said that a renewed groundswell of support for stricter laws will be needed to compel Congress to debate the issue again. Supportive lawmakers are waiting to see whether a new public campaign by such interest groups and the White House will put pressure on senators who voted no on the legislation to at least reconsider their stance, but they admit that the new push could take months to succeed.

In hopes of keeping support for the issue alive, Vice President Biden planned to meet Monday with faith leaders at the White House to discuss the gun legislation.

Philip Rucker contributed to this report.

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