HOUSTON —  Weeks after the Senate defeated a proposed expansion of background checks on gun purchases, the annual conference of the National Rifle Association here has a celebratory atmosphere.

NRA members derailed “what looked like an unstoppable freight train,” Sen. Ted Cruz, R-Texas, said Friday after taking the stage to a sustained standing ovation. “The target of their legislation is not violent criminals,” he said. “The target of their legislation is law-abiding citizens.”

Yet as the festivities began, gun-control advocates have been swarming town halls, organizing petitions and buying local ads to pressure senators from Alaska to New Hampshire to reconsider the measure that failed by six votes on April 17. They also descended on Houston to protest outside the NRA event.

In Washington, the efforts inspired by the Dec. 14 slaughter of 20 children in an elementary school shooting in Newtown, Conn., appeared to be gaining some ground.

Sen. Max Baucus, D-Mont., who voted against the measure and then announced he would retire, said in a statement this week he would “evaluate” any new gun-control attempts. Sen. Joe Manchin, D-W.Va., who wrote the defeated background-check measure with Sen. Pat Toomey, R-Pa., told reporters April 23 that he is trying to craft such a compromise.

President Obama will “press ahead” for legislation and will explore taking executive actions, his press secretary, Jay Carney, told reporters Friday.

Texas Gov. Rick Perry, R, a lifetime NRA member who has an A-plus rating from the group for his support of gun rights, used his remarks before the Houston gathering to criticize efforts to expand background checks.

“While they may keep our president scoring political points, they do nothing but make it harder for law-abiding Americans to own guns,” Perry said, drawing whistles and applause from the crowd. That “makes it easier for predators to prey upon the defenseless.”

A new batch of polls, including some released Thursday, show that senators who favored expanding background checks are enjoying a bump in popularity. The approval rating for Toomey has climbed to 48 percent in a poll conducted April 19-24 by Quinnipiac University, up from 43 percent in March.

Those findings were in contrast to other recent polls showing a decline in support for those voting against the bill. An April 29 survey by Public Policy Polling, a Democratic- leaning group, found that the approval rating for Sen. Lisa Murkowski, R-Alaska, had fallen to 46 percent from 54 percent in February.

The NRA and other pro-gun ownership groups are countering, running ads of thanks in the states of their Senate supporters. The approximately 70,000 activists expected to attend the Houston convention were hearing calls for action Friday from at least four Republican prospective presidential candidates: Cruz, Perry, Louisiana Gov. Bobby Jindal and former Pennsylvania Sen. Rick Santorum.

The test for gun-control advocates is whether they can sustain momentum and convert their fervor into political wins, either by resurrecting and passing a gun-control bill this year – a rare occurrence on an issue that generates passion on both sides, or by ousting its opponents next year at the ballot box.

Supporters of tougher background checks are borrowing tactics from the anti-tax tea party groups that were galvanized to action in 2009 by opposition to Obama’s health-care law and helped restore Republicans to control of the House in 2010.

Mayors Against Illegal Guns protested Thursday outside the Phoenix office of Sen. Jeff Flake, R-Ariz. A PPP poll released this week showed the freshman senator’s approval rating stood at 32 percent, compared with 52 percent who disapprove.

In a posting on his Facebook page, Flake said: “Nothing like waking up to a poll saying you’re the nation’s least popular senator. Given the public’s dim view of Congress in general, that probably puts me somewhere just below pond scum.

“Now, notwithstanding the polling firm’s leftist bent, I would assume that my poll numbers have indeed taken a southerly turn since my vote against the Manchin-Toomey background check proposal. It was a popular amendment, and I voted against it,” Flake wrote, adding a link to a local story explaining the amendment’s complexities.

Earlier this week, Erica Lafferty, the daughter of the principal killed at Sandy Hook Elementary School in Newtown, confronted Sen. Kelly Ayotte, R-N.H., the only senator from the Northeast to oppose the measure.

She recalled Ayotte’s stated concern that the background checks would be a burden on gun owners and sellers.

“I’m just wondering why the burden of my mother being gunned down in the hall of her elementary school isn’t as important as that?” Lafferty asked the senator, before storming out of the April 30 town hall.

Lafferty is expected to be in Houston, where gun- control advocates plan to read the names of shooting victims outside the NRA conference during the next three days.

The Manchin-Toomey amendment would have required background checks for anyone purchasing a firearm at a gun show or over the Internet. It needed 60 votes; it received 54. Thirteen senators who voted against the proposal are up for re-election in 2014. Ayotte’s term expires in 2017.

In addition to agitating at town halls, gun-control advocates have purchased television and radio ads to criticize senators who voted against background checks.

Americans for Responsible Solutions, a political group helmed by shooting victim and former Rep. Gabrielle Giffords, D-Ariz., debuted radio ads targeting Ayotte and Senate Minority Leader Mitch McConnell, R-Ky.

“We watched. We listened. We felt it. Newtown,” an announcer says. “But Senator McConnell won’t listen to us.”

Mayors Against Illegal Guns, the best-funded outside group pressing for gun control, also released an ad aimed at Ayotte. The group is led by New York Mayor Michael Bloomberg, founder and majority owner of Bloomberg News parent Bloomberg LP.

The NRA is running ads in New Hampshire to support Ayotte, and some at her town halls hoisted signs saying they are with her. The ad thanks Ayotte for her vote and praises her for “protecting our kids” because she wants to shore up the mental-health system rather than tightening gun controls.

Progressive Change Campaign Committee, a political group that typically supports Democrats, spent $50,000 to air a TV ad in Montana and Washington asking Baucus to reconsider his position on background checks.

“Now that you’re retiring, please put Montana first,” a woman says at the close of the spot.

That group touted Baucus’ statement Thursday as “huge,” though the senator makes clear that he would reconsider his position “based on the feedback he gathers from the people of Montana.”

Progressive Change has also spent $100,000 on full-page ads in the hometown newspapers of Democrats Baucus, Arkansas Sen. Mark Pryor, Alaska Sen. Mark Begich and North Dakota Sen. Heidi Heitkamp. Begich and Pryor are running in 2014.

In Houston, hundreds of NRA supporters, many dressed in Second Amendment and flag-themed apparel, walked through hallways where the group’s “stand and fight” motto is plastered on banners and souvenirs. Conservative TV and radio host Glenn Beck headlines a rally by that name here Saturday.

“I was so proud of the American public, and the NRA, for putting enough pressure on our politicians,” Neil Solt of Cypress said Thursday while waiting to have his World War II heirloom guns appraised at a pre-convention event.

Bud Clark of Magnolia predicted more tries at expanding background checks would be fruitless.

“What we already have is enough, and we are not going to change our minds about that,” he said as he awaited an evaluation of a 1918 German Luger pistol.