Former Sen. John E. Sununu has officially decided against running for Senate from New Hampshire, according to the New Hampshire Union Leader, setting up what will likely be a contentious primary for the chance to challenge Sen. Jeanne ShaheenCynthia (Jeanne) Jeanne ShaheenQuestions loom over Franken ethics probe State Dept. spokeswoman acknowledges 'morale issue' Democrats scramble to contain Franken fallout  MORE (D).

At least one potential candidate, State Senate Majority Leader Jeb Bradley, told The Hill that he's likely to run.

Asked whether rumors in the state that he's 90 percent in for a Senate race were true, Bradley confirmed he's leaning towards it.

"There's a lot of speculation. I can't deny that that's a fact, but as I keep repeating, day job comes first," he said, reached shortly after Sununu's decision went public.

Calling him a "friend," Bradley said that Sununu, with whom he served in Congress, "was a great public servant."

Bradley insisted that, for the next few months, his focus is on the state's legislative session, which ends June 30. He said there are "significant issues with regard to the implementation of ObamaCare" in New Hampshire that he hopes to tackle, and indicated he plans to push back against Gov. Maggie Hassan's (D) budget.

The focus on ObamaCare could be an early indication of the argument Bradley, a two-term U.S. congressman and longtime state legislator, plans to make in the Senate race.

A Republican strategist familiar with Bradley's efforts said he has reached out to Republican donors in the state, though Bradley said only that he's "always talking to people all the time about the future of the Republican Party...and how we can turn things around in New Hampshire in 2014."

But he may face a fierce fight from former Rep. Frank Guinta, who spokesman Mike Dennehy says is looking more seriously at the seat now that Sununu has decided against it.

"Frank is considering all of his options equally, but he was received overwhelming encouragement from top Republicans and donors in New Hampshire to run for U.S. Senate," he told The Hill, and indicated that Guinta was likely to make his decision before the summer "so campaigns can begin organizing."

Guinta could also run to retake his old seat, in New Hampshire's 1st district, as Rep. Carol Shea-Porter (D) is considered vulnerable by Republicans. But he appears to be leaning towards the Senate.

A third potential candidate, wealthy businessman and conservative activist Fred Tausch, may be less likely to run, but he's expected to make a decision by June.

And former Massachusetts Sen. Scott Brown (R) indicated he may be interested in a run. If he were to launch a campaign, he'd be a formidable fundraising force, and would at least be able to complicate Shaheen's reelection bid by drawing millions to the race. He'll be appearing at five events throughout the state over the next five months, stoking speculation that he may be building support for a possible bid.

But he'd be vulnerable to carpetbagging attacks, and seems at this point more likely to spend some time in the private sector and as a Fox News commentator before perhaps running for governor in Massachusetts in 2014.

A primary between Bradley and Guinta would be battle enough for the Granite State, however. The two have a contentious past — Guinta worked for Bradley during his time in Congress, but when Guinta ran for Bradley's old seat, Bradley didn't endorse him and instead suggested he should drop out of the race at one point.

New Hampshire Republicans believe bombs could fly if the two do meet in a primary, but they insist they're not concerned at the prospect.

"The Republican Party typically embraces primaries. Primaries are a good thing. They help us excite the base, help us talk to a broader range of people, they get our energy up," said Granite State GOP strategist Jim Merrill, who has worked previously with Bradley.

Merrill also noted that both Guinta and Bradley would be prepared if they were to meet each other in a primary contest.

"Jeb's no stranger to a tough primary, and neither is Frank. They've both been in them, and they've both run strong campaigns," he said.

The New Hampshire Democratic Party dismissed the two candidates as "failed Tea Party candidates" who would be defeated in their Senate run as they have been in previous races.

"Get ready for the NHGOP D-team of failed former Congressmen Jeb Bradley and Frank Guinta.  New Hampshire Republicans know that Guinta and Bradley's records are electoral black holes - that is why they spent the last week openly salivating over the prospects of a carpetbagger run by rejected Massachusetts politician Scott Brown," said NHDP spokesperson Harrell Kirstein.

But New Hampshire Republicans feel optimistic about their chances at defeating Shaheen, citing the party's majority in the state Senate and the fact that GOP presidential nominee Mitt Romney kept President Obama's lead last cycle down to low single-digits.

Shaheen, however, remains popular in the state, with a recent poll showing her at a near-career-high popularity level, and she announced just this week that she brought in $1.2 million in the first quarter of the year, a strong sum for an incumbent looking at reelection.