Crucial Senate battle heating up

(CNN) - Former Sen. Scott Brown of Massachusetts will go up Monday with his first television commercial in his Republican bid for the Senate in neighboring New Hampshire.

The launch of the ad, coming just four days after Brown formally kicked off his campaign, is another sign that if he wins his party's nomination, his GOP challenge against incumbent Democratic Sen. Jeanne Shaheen could turn the contest in the Granite State into one of the most high profile and expensive Senate races in the country.

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And word of the spot comes as a new poll indicates Shaheen's lead over Brown in a possible November election showdown is shrinking to single digits.

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The ad, first reported by WMUR's James Pindell, highlights Brown's recent listening tour throughout New Hampshire.

"Scott Brown has almost 300,000 miles on this truck," says the narrator says in the spot. "Over the last few weeks it's taken him all across New Hampshire, listening, learning – and what he's learned is pretty simple: People want an America that leads the world again, a health care system that works for new Hampshire and more good jobs."

Brown has made opposition to the health care law a key part of his push for the Senate. His campaign says the commercial will run on WMUR, the main television station in the state, but aides wouldn't share details on how much money they were putting behind the spot, or how long it would run.

Shaheen has yet to run a TV commercial, but her campaign has gone up with radio ads. The real action in the campaign ad wars in New Hampshire has come from national outside groups.

Two of the biggest players when it comes to outside spending, Americans for Prosperity (which is backed by the big bucks of the billionaire industrialist Koch Brothers) and American Crossroads (which was co-founded by Karl Rove), have poured more than $1 million into the race, mostly to attack Shaheen for her support of the health care law.

And the Ending Spending Action Fund, a pro-Republican outside group, went up this week statewide with a TV commercial that used a clip of Brown from four years ago slamming the new federal health care law. The spot ends with the narrator saying that "Scott Brown was right on Obamacare then, he's right for New Hampshire Now. The group put out a spot last year in an effort to convince Brown to run for the Senate in New Hampshire.

Meanwhile, the pro-Democratic Senate Majority PAC spent almost $200,000 to run ads supporting Shaheen.

Poll indicates single digit race

According to a new WMUR/University of New Hampshire Granite State Poll, Shaheen holds a 45%-39% advantage over Brown among likely voters in a potential general election matchup. Shaheen's six percentage point advantage is down from a 10 point lead in January. Fourteen percent are undecided in the new survey.

The incumbent had a double digit advantage in two polls conducted last month. According to a Suffolk University/Boston Herald survey, Shaheen had a 52%-39% lead among New Hampshire voters. And the senator was up 50%-38% over her potential GOP challenger in an American Research Group survey conducted around the same time.

Brown joins three other Republicans who are running for their party's Senate nomination in New Hampshire: former U.S. Sen. Bob Smith, former state Sen. Jim Rubens, and conservative activist Karen Testerman. The winner of the September 9 primary will face off against Shaheen, who also served for six years as the state's governor.

In the new poll, Shaheen leads Smith by 14 points, Reubens by 21 points and Testerman by 23 points. But in all four of the potential November showdowns, the incumbent's under 50%. And the high rate of undecideds may also be troubling to the senator, as political experts generally believe that undecided voters tend to break against the incumbent.

But the survey indicates that Shaheen is viewed much more favorably than Brown. The senator has a plus 14% net favorablility, compared to Brown's minus 10%. But Shaheen's favorable opinion among crucial independent voters has dropped significantly.

Brown kicks off campaign

Brown formally kicked off his campaign Thursday at an event in Portsmouth. The sea coast city's setting emphasizes his roots in the Granite State. His mother lives in the vicinity, he spent a lot of his childhood in the area, and he was born just across the Piscataqua River, in Kittery, Maine.

"Our campaign for the U.S. Senate begins not far from where my life began. I was born right over there at the Naval Shipyard. When my Mom was a young woman, she was a waitress in Hampton Beach, my Dad an airman at Pease. They met, fell in love, and a year or so later I came along. When they carried me home, it was to a house not far from here on Islington Street," Brown said.

Since late year, when he began considering a Senate bid in New Hampshire, Brown's been highlighting his ties to the Granite State, to push back against Democrats' characterizations of him as a "carpetbagger" from Massachusetts.

Shaheen's big numbers

As Brown was preparing for his kickoff in Portsmouth, Shaheen reported her best fundraising quarter in her nearly six years in the Senate. Her campaign announced that they raised more than $1.5 million the past three months. They say that brings to $7.3 million the total amount they've raised so far this election cycle, and that they've got $4.35 million cash on hand. The campaign adds that 27,000 people donated to Shaheen in the first quarter, up 12,000 from the previous three months.

"Our campaign is proud of all the grassroots support our campaign has generated to date and we're confident we'll have the resources we'll need to win this November, regardless of whom Republicans nominate to run against Jeanne Shaheen," said her campaign spokesman Harrell Kirstein.

From Massachusetts to New Hampshire

Brown, then a little-known state senator, in Massachusetts, scored an upset victory in a special election in January 2010 to serve the final three years of the term of the late Democratic Sen. Ted Kennedy, who had died the previous summer. Brown lost his bid 2012 re-election bid for a full six-year term to Democratic challenger Elizabeth Warren.

Last year, Brown passed on running in a special election in Massachusetts to fill the term of John Kerry, who left the Senate to become secretary of state. And at the time, Brown also announced that he wouldn't make a 2014 bid for an open governor's seat in the Bay State.

Brown made a number of speaking appearances at GOP events in New Hampshire last year, where he spent much of his childhood and where he owned a vacation home. Last fall, in another hint about a possible run, he dropped the 'MA' from his Twitter handle. A few months later, he sold his home in Massachusetts and moved his residency north to the Granite State.

Last month, Brown announced that he was forming an exploratory committee, which allowed him to raise money and hire staff for a Senate bid. He immediately began a listening tour across New Hampshire. And last Friday CNN confirmed that a former longtime close aide, Colin Reed, had left his job as deputy communications director for New Jersey Gov. Chris Christie to serve as Brown's campaign manager.

If Brown ends up winning the GOP's September primary, it could expand the map for Republicans. Democrats hold a 55-45 majority in the Senate (53 Democrats and two independents who caucus with the party), but are defending 21 of the 36 seats up in November, with half of those Democratic-held seats in red or purple states, like New Hampshire.