Alex Brandon / AP

In this file photo, Sen. Scott Brown, R-Mass., speaks during a media availability, on Capitol Hill. Brown, who was defeated in his re-election bid, said Friday, Feb. 1, 2013 that he will not run for the Senate seat vacated by John Kerry, who was named secretary of state.

Updated 1:51 p.m. - Former Massachusetts Republican Sen. Scott Brown, won't look to reclaim a spot in the Senate in this summer's special election to replace outgoing Sen. John Kerry.

Brown decided against running in the special election, a Republican official told NBC News on Friday. The decision strengthens Democrats' chances of holding the seat in the special election in the June 25 special election.

"I was not at all certain that a third Senate campaign in less than four years, and the prospect of returning to a Congress even more partisan than the one I left, was really the best way for me to continue in public service at this time. And I know it’s not the only way for me to advance the ideals and causes that matter most to me," Brown said in a statement. "That is why I am announcing today that I will not be a candidate for the United States Senate in the upcoming special election."

The special election would have been Brown's third since his initial January 2010 election to the Senate, when he bested Democratic favorite Martha Coakley in an election to fill the seat of the late Sen. Edward Kennedy. Brown's election came at the height of the fight over health care reform in Congress, and his victory was seen as the advent of the political influence of the Tea Party movement.

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Brown styled himself as a relative moderate during his time in the Senate, breaking with Republicans to approving an overhaul of financial regulations and repeal "Don't Ask, Don't Tell," among other issues. A former state senator, Brown was seen as the relative favorite to win re-election during a full term in this fall's general election until Democrats managed to convince Elizabeth Warren to enter the race. Warren beat Brown, 54 to 46 percent, in November.

Brown was seen as having an advantage had he decided to attempt to reclaim a Senate seat. A number of Democrats have endorsed Rep. Edward Markey for the Senate nomination, though Rep. Stephen Lynch will challenge Markey in the primary. Republicans maintain the discord in the Democratic primary could improve their chances of winning the election.

Elizabeth Warren's plum speaking slot at next month's Democratic National Convention has prompted misgivings among some centrist Democrats, who worry the Massachusetts Senate candidate could turn off independent voters.

Democrats announced this week that they had tapped Warren, the former consumer financial protection czar who's challenging Sen. Scott Brown (R-MA) this fall, to deliver a prime time address before a national television audience. A popular figure among progressive activists, Warren has built a reputation as an outspoken critic of the excesses of Wall Street — a kind of populism Democrats are hoping to showcase at their convention.

But some members of the party wonder if selecting a figure like Warren — whom Republicans have sought to characterize as an out-of-touch elitist and cloistered Harvard professor — might hurt the party on a national level. She will speak the evening of Weds., Sept. 5, before a famed centrist Democrat: former President Bill Clinton.

“Having someone from the more extreme wing of the party, being given the primetime slot sends the wrong message to people in the middle who are legitimately up for grabs in this race," said Pennsylvania Rep. Jason Altmire (D-PA).

Altmire is among the dwindling ranks of the Blue Dog Coalition, the group of moderate Democrats in the House. These lawmakers typically hail from rural or working class districts and favor more fiscally responsible policies and permissive gun rights.

They've seen their representation in Congress shrink, though. The caucus had 54 members before the 2010 midterm elections, which shrunk to 25 this Congress. At least seven of them — including Altmire, who lost a primary to a more liberal Democratic Rep. Mark Critz (PA) — won't be returning to Washington next year.

Altmire said that while Warren's progressivism might play well in Massachusetts, the party might be better-served by a different prime time speaker.

"If you’re trying to win over people from the center — moderates and centrists who could go either way — I would guess there are other faces you could put forward who would be better for that," he said.

Another retiring Blue Dog, Oklahoma Rep. Dan Boren, argued for better geographic representation in the convention's prime speaking slots.

“If we are going to become a big tent, we need language that speaks to fiscal responsibility, we need some speakers who are from the South, we are already winning in the coastal areas of the country,” Boren told NBC News. “if you’re going to speak to the 4 percent [of undecided swing state voters] you’re going to want somebody who can appeal to independents, I think it would be better to have somebody from more Middle America.”

But other Democratic moderates expressed a greater comfort level with Warren relative to some of their colleagues.

Virginia Rep. Gerry Connolly (D), who won re-election by only 981 votes last cycle, called Warren a "very engaging speaker" who has a "real ability to speak to the lay person about what the underlining dynamics are in the economy."

That's precisely what Democrats are hoping to project with Warren's speech. From a working class background in Oklahoma, Warren speaks often about themes of opportunity and strengthening the middle class. To that end, Connolly said he thought Warren would “highlight advocacy for the middle class.”

Ohio Rep. Tim Ryan (D) saw particular opportunity for Warren to appeal to women: "She will definitely speak to working class women, and I don’t think she’s going to turn anybody off. She comes across as pretty tough; I don’t see her coming off as a heady intellectual, it’s inner toughness about taking on the banks.”

Prime time speakers at party conventions are usually selected to help broaden the party's appeal to voters who don't adhere to strict political orthodoxies. The choice of San Antonio Mayor Julián Castro to keynote the Democratic convention is a good example of that.

One Democratic operative NBC News that Warren could do that, too, but, “she carries a risk."

"I’d say she’s high risk, high reward," said the operative. "People could relate to her down with the 'greedy guys' talk, or see her as polarizing and part of the problem.”

But another retiring Blue Dog, North Carolina Rep. Health Shuler, expressed concern that Democrats could risk seeming as though they're uninterested in moderates by putting Warren front-and-center.

“I hope in time, Democrats realize in order for us to appeal to more voters, we need to highlight more moderates, not show just the far left of the party but in fact give people an opportunity to see we are a big tent," he said, pointing to the GOP's struggles with the Tea Party as a cautionary tale. "That helps us with independents; we don’t want to be pushing out moderates just like the Republicans are doing.”

MASSACHUSETTS: The story that just keeps on keepin’ on…  “Democratic Senate candidate Elizabeth Warren acknowledged for the first time late Wednesday night that she told Harvard University and the University of Pennsylvania that she was Native American, but she continued to insist that race played no role in her recruitment,” the Boston Globe writes. 

Warren said in a statement, “At some point after I was hired by them, I . . . provided that information to the University of Pennsylvania and Harvard. My Native American heritage is part of who I am, I’m proud of it and I have been open about it.”

The Globe does point out: “Two key people who recruited her to Harvard have said they did not know of her purported heritage or take it into account when hiring her. The school did not promote her as a Native American when she was hired, despite the fact that it was under intense pressure to diversify its faculty with more minorities.”

The Massachusetts Senate race took a bit of a sharper turn Wednesday, when Sen. Scott Brown (R) accused Democratic opponent Elizabeth Warren of harboring an "elitist attitude" by way of communicating her policies.

Following a speech on the need for bipartisanship in Washington, in which Brown emphasized his work across the proverbial aisle, the senator took one of his toughest shots personally at Warren.

Asked about a release by his campaign, which labeled Warren an "elitist hypocrite" for declining to pay a slightly higher income tax rate in her Massachusetts filing, Brown told reporters:

"Listen, the bottom line is the way that she's approaching things, knowing better than others how to do things. The federal government can do things better than individual businesses and individuals, I think there is an elitist attitude there in the way that she's communicating to us as citizens and telling us how to do things, who should be taxed, who should not be taxed. I'm going to continue to do what I've always done and that's find solutions.”

That marks a bit of a nastier turn in this race, in which both candidates have emphasized good governance and reformist policies versus each other.

Brown also defended his own solicitation of donations from the Wall Street and financial services community, pointing to the large concentration of that sector in Massachusetts. But he also took a shot at Warren for raising money from liberal heavyweights, too.

"I'm raising money like every other member of the delegation," Brown said. "The president has taken more money than anybody, as you know, and I have raised money on Wall Street and from financial services industries.  As you know, we have the 2nd highest financial industries in the country in Massachusetts. And she's raised money from Wall Street and from George Soros who's a convicted felon, an insider trader. So I have to chuckle at that.”

Matt Loffman contributed.

Massachusetts Sen. Scott Brown (R) is going further in linking himself to President Obama in a new radio ad supporting his re-election.

NBC's Kelly O'Donnell flags this new radio ad in Massachusetts in which Brown, in his own voice, talks up his bipartisan initiatives and the pride he felt in attending a signing ceremony at the White House in which Obama signed a vets' jobs bill that Brown had authored.

"Standing with President Obama on the day he signed it into law was another one of those great experiences," Brown says in the ad. "Whatever else may separate us, we are Americans first. To me, that means we need to work together now."

Steven Senne / AP

Sen. Scott Brown, R-Mass., addresses an audience during ceremonies held to honor fallen Woburn Police Officer John "Jack" Maguire, in Woburn, Mass.

First Read has written in the past about Brown's efforts to embrace Obama as he seeks a full Senate term in deep-blue Massachusetts. His attendance of the signing ceremony referenced in the ad, along with another signing to ban insider trading on Capitol Hill, was seen as part of an effort to further that linkage in the mind of voters.

Democrats, meanwhile, have sought to tie Brown to Mitt Romney, the former Massachusetts governor whose political organization is heavily intertwined with Brown's.