Following the Easter recess, the U.S. Senate will begin debating a package of proposed gun control regulations, including a measure that calls for comprehensive background checks for would-be buyers.

The proposed legislation, which would expand the use of criminal background checks beyond the gun shop, sits at the center of a targeted ad campaign launched this week by Mayors Against Illegal Guns.

The $12 million television-focused effort is aimed at senators — Democrats and Republicans — in 13 key states across the country, including Ohio, North Carolina and Arizona.

Pennsylvania is also a focus of the bipartisan blitz — specifically, Republican Sen. Pat Toomey.

Democrat Bob Casey, Toomey's counterpart, now supports background checks. He changed his stance following the mass killings at Sandy Hook Elementary in Connecticut.

"We've sort of conceded public debate of these issues to the NRA and people who are advocates for less and less gun regulation," said Lancaster Mayor Richard Gray, the Pennsylvania chair of Mayors Against Illegal Guns. "This is just part of us getting politically active on the other side of the issue where we, frankly, represent the majority of people in this country."

A recent Quinnipiac University poll found that nearly 90 percent of Americans, including gun owners, support comprehensive background checks.

In Pennsylvania, about 95 percent of those polled favor background checks.

"It's, one, an issue whose time has come. And, two, that if the opponents of any reasonable gun regulation would take the time to listen to what they're saying, this is in fact does exactly what they want," Gray said. "In other words, it enforces the laws on the books right now."

"Responsible," the 30-second spot running in Pennsylvania starting Wednesday, shows a bearded hunter on the edge of his truck, holding a shotgun. He tells viewers that he supports the Second Amendment and comprehensive background checks.

"For me, guns are for hunting and protecting my family," he says. "I believe in the Second Amendment and I'll fight to protect it. But with rights come responsibility. That's why I support criminal background checks."

Efficacy of ad remains to be seen

Despite public support for the measure, it's unclear how effective the ad, bankrolled by billionaire New York Mayor Michael Bloomberg, will be at influencing lawmakers.

Stephen Medvic, associate professor of government at Franklin & Marshall College in Pennsylvania, said it's unlikely the campaign will have an impact on Toomey.

"When it's pretty clear where a senator stands on something, either because the party's base has a very strong position on it or just ideologically, you know where they stand, it would be very difficult for an outside group like this to change a vote — in fact, nearly impossible," he said.

James Thurber, a professor of government at American University in Washington, said targeted campaigns, such as Bloomberg's, can be effective if they're multifaceted.

"A target advertising campaign on television is important in these kinds of battles and, in fact, it's an important element of this and I think it'll be a positive thing," said Thurber. " But these campaigns also have to have people on the ground, well-organized, putting pressure on members of Congress."

Toomey could not be reached for comment.

During his 2010 campaign, the first-term lawmaker said that his "idea of gun control is a steady aim."

Congress will be back in session April 8.