The commercial is an unambiguous appeal to gun owners: A middle-aged hunter, rifle in hand, vows that he will fight to protect the Second Amendment. But in a sensible, father-of-the house tone, he also urges voters to support comprehensive background checks, “so criminals and the dangerously mentally ill can’t buy guns.”

The man behind the advertisement is not known for his kinship with the gun crowd: New York City Mayor Michael Bloomberg, the nation’s fiercest advocate of restrictions on firearms since the December rampage at Sandy Hook Elementary School in Newtown, Conn.

Determined to persuade Congress to act in response to that shooting, Bloomberg on Monday will begin bankrolling a $12 million national advertising campaign that focuses on senators who he believes might be persuaded to support a pending package of federal regulations to curb gun violence. The ads, in a dozen states, will blanket those senators’ districts during an Easter congressional recess that is to be followed by debate over the legislation.

Among those targeted: North Carolina’s Sen. Kay Hagan.

Bloomberg’s commercials make no mention of an assault weapons ban once sought by the White House and its allies, instead focusing on the more achievable goal of universal background checks.

The mayor’s advertising blitz, which will saturate television screens in states including Ohio, Pennsylvania, North Carolina and Arizona, represents by far the biggest escalation of Bloomberg’s attempts to become a one-man counterweight to the National Rifle Association in the political clash over guns.

“The NRA has just had this field to itself,” Bloomberg said. “It’s the only one that’s been speaking out. It’s time for another voice.”

After months of wrangling, the current package of Senate legislation would expand background checks for gun buyers, increase penalties for people who buy firearms for those barred from owning them and would give law enforcement new tools to combat illegal gun trafficking, a longtime goal of Bloomberg’s.

Given the mayor’s role in contributing to the ouster of an NRA-backed candidate in an Illinois congressional race a few weeks ago, his push carries an unmistakable threat to those who vote against the bills.

The ads are directed at prominent Democratic and Republican senators in both swing states and partisan precincts. Among Bloomberg’s targets are some of the Senate’s most vulnerable Democrats, including Hagan, Mary Landrieu of Louisiana and Mark Pryor of Arkansas, for whom the gun issue is particularly problematic because they will need Republican votes to win re-election.

Some of the senators, such as Dean Heller of Nevada, Rob Portman of Ohio and Patrick Toomey of Pennsylvania, all Republicans, represent swing states where voters are divided over guns. Other Republicans would seem to be out of reach for Bloomberg: Saxby Chambliss and Johnny Isakson of Georgia, Daniel Coats of Indiana and Jeff Flake of Arizona.

On Saturday, Hagan's office said the senator "always votes for North Carolina first, and on this issue she has heard from many constituents who consistently ask her to protect their second amendment rights and use commonsense."

"As the debate on this issue moves to the Senate floor, Senator Hagan will continue seeking input from North Carolinians while focusing on legislation that protects the rights of responsible gun owners and has a realistic chance of passing to make real progress in preventing tragedies like the one at Sandy Hook," said Hagan spokeswoman Sadie Weiner.

The commercials urge support for the measure to require background checks for nearly all firearms purchases, not just those in gun stores, the most debated element of the legislation and a coveted goal of gun control advocates.

Bloomberg has singled out Flake, who already voted against the expansion of background checks in the Senate Judiciary Committee, by producing a special, scolding commercial aimed at Arizona. “Flake’s vote,” the ad declares, equals “no background checks for dangerous criminals.”

The mayor, who over the years has spent tens of millions of dollars to support his favored candidates, holds the power to use his super PAC to wield influence in the midterm congressional elections next year and beyond. He said he would heavily favor “candidates who will stop people from getting killed.”

“There is an easy measure of how you decide who those are,” he said, noting that gun rights groups rate lawmakers. “The NRA keeps score of it for you. They are public information.”

To those who might fear his financial might, he added: “If they pass sensible gun legislation, there is not an issue.”

The NRA plans to roll out its own lobbying campaign, using print and broadcast advertising to reach lawmakers during the recess. But its leaders said that their investment was unlikely to rival the intensity of Bloomberg’s spending, to be carried out through Mayors Against Illegal Guns, a group he co-founded.

“Can we match Mayor Bloomberg dollar for dollar?” asked Chris Cox, the group’s chief lobbyist. “No one can. We don’t have to.”

He predicted that voters and senators would resist a message from an out-of-state magnate who is associated with government limits on soda and salt.

“What he is going to find out is that Americans don’t want to be told by some elitist billionaire what they can eat, drink and they damn well don’t want to be told how, when and where they can protect their families,” Cox said.

Thomas Mann, a congressional scholar at the Brookings Institution, agreed that Bloomberg “is not popular in many of the states he is going into right now.”

He said that $12 million in advertising was unlikely to influence the outcome of the legislation unless lawmakers were convinced that Bloomberg would open his wallet again after the vote – both to reward those who supported the bill and to punish those who did not. “That is absolutely key,” Mann said.

Flake, for example, was just elected and will not face voters again until 2018.

Bloomberg said that “sausage and the law aren’t pretty the way they are made.”

But he is eager to seize what he can.

“I think you’ve got as good a chance as we’ve ever had,” the mayor said. FRANCO ORDONEZ CONTRIBUTED