NASHUA, N.H. (AP) — In a move cheered by Republicans nationwide, former Massachusetts U.S. Sen. Scott Brown on Friday declared he wants to "stop complaining and get involved again" by formally joining the race against Democratic U.S. Sen. Jeanne Shaheen.
The longtime Massachusetts resident, who recently moved into his seacoast New Hampshire vacation home, launched an exploratory committee to enter the Senate race during a Republican conference in Nashua, ending months of speculation about his intentions.
While Brown has yet to file formal candidacy papers, his decision all but assures the GOP will have a top-tier contender who, win or lose come November, helps his party's national push to claim the Senate majority — a shift that could fundamentally reshape the final two years of President Barack Obama's presidency.
Underscoring the significance of Brown's move, the Washington-based Republican ally American Crossroads immediately announced plans to invest $650,000 in a television advertising campaign against Shaheen beginning next week. Strategists on both sides said the contest could quickly become the most expensive in state history.
Brown, facing a packed hotel ballroom Friday evening, said his wife told him he should run for the U.S. Senate in New Hampshire if he really wants to make a difference.
"Honey, you are right," he said just before the crowd gave him a standing ovation. "I'm going to stop complaining and get involved again."
Recent polls give Shaheen a solid lead in a prospective matchup, but Brown's near-universal name recognition in a Massachusetts border state and his national fundraising network makes him a serious contender on Day 1.
Brown, whose move to his vacation home satisfies a state residency requirement, rose to national prominence by winning the 2010 special election to replace the late Massachusetts Democratic U.S. Sen. Ted Kennedy. But he was soundly defeated in his first re-election test against Democrat Elizabeth Warren in 2012. His first race, like this year's New Hampshire contest, hinged on the popularity of Obama's health care overhaul.
Brown declined to enter a 2013 special U.S. Senate election in Massachusetts, citing the strains of running a third Senate campaign in less than four years and partisan gridlock in Washington.
"I'm tired of the blaming," Brown said Friday as he talked up his New Hampshire connections. "I'm tired of the divisiveness."
Earlier in the day, Fox News Channel formally cut ties with Brown, who had recently renewed a contract to serve as a paid political contributor. Fox and other networks regularly feature former politicians but don't continue paid relationships once they become candidates.
Brown's decision overshadowed appearances by other high-profile Republicans on the first day of the Northeast Republican Leadership Conference, which features prospective presidential candidates and other GOP leaders looking to court New Hampshire voters and put their stamps on party affairs.
Democrats had scoffed at a prospective Brown candidacy, noting that he also was considering a 2016 presidential campaign. Brown canceled plans to visit Iowa next month and downplayed his White House aspirations on Friday.
New Hampshire Democratic Party spokesman Harrell Kirstein said Brown "is for Scott Brown and the Wall Street and Big Oil millionaires that back him, not New Hampshire."
"If he manages to survive a Republican primary against Republicans who are actually from New Hampshire," Kirstein said, "he'll have an even tougher general election against Jeanne Shaheen."
National Democrats already have their hands full defending more vulnerable Democratic incumbents across the country as they fight to retain their six-seat Senate majority this fall. With finite resources, they would rather not devote additional time or resources to a New Hampshire seat that was supposed to be safe.
National Republican strategist Brian Walsh said it's difficult to overestimate the impact Brown's announcement has on the U.S. Senate race map and Republicans' hopes of winning back the Senate this year.
"Senate Democrats are now playing defense in roughly a dozen states and, at a minimum, they'll now have to spend millions of dollars in New Hampshire, which is money they won't be able to spend in other races," Walsh said.
Even before American Crossroads' announcement, conservative groups began pouring money into anti-Shaheen advertising earlier in the year focusing particularly on her support for Obama's health care overhaul.
Brown had agreed to a so-called People's Pledge in Massachusetts during his 2012 Senate contest, essentially blocking outside groups from getting involved in the race. It's unclear if he'll agree to such a pact this time.
AP television writer David Bauder in New York contributed to this report.