Sen. John Sununu (R-N.H.) could actually be in his toughest race to date.

And that’s a high standard, considering Sununu won a seven-way House primary in 1996 by fewer than 500 votes, and defeated an incumbent Senator in the 2002 Republican primary and a popular sitting governor in the general election later that year.

Sununu is nothing if not battle-tested. So why are Republicans in the Senate and at home privately so nervous about his campaign?

Probably because most publicly released polls show him down double digits to his challenger, former Gov. Jeanne Shaheen (D), in a state where the Democratic wave hit particularly hard in 2006. Both Congressional seats, the state House and the state Senate all flipped to the Democrats two years ago, and the Democratic governor won re-election by 48 points.

But it also may have something to do with the fact that Sununu only recently put a full campaign team together, despite the fact that he is one of the most vulnerable Senate incumbents in the country this cycle.

In an interview late last week, however, Sununu expressed confidence in his re-election prospects. “I was outspent 3-1 and I won the primary” in 2002, he said. “In the general election, I was outspent 2-1, and I won. It was arguably the highest-profile race in the country that year. I know what it is to run and win a tough campaign.”

New Hampshire Republican Party Chairman Fergus Cullen, who supported Sununu for Senate when he challenged then-Sen. Bob Smith (R) six years ago, said Sununu has “been tested so very many times.”

“One of the reasons that we are so confident in him this year is that unlike so many other Senators, he has not had an easy political life,” Cullen said.

Sununu said his plan has always been to ramp up his campaign staff and consulting team in the second financial quarter of this year, especially with the presidential campaign dominating the political scene in New Hampshire until January.

Yet in the age of the years-long campaign, Shaheen started reacquainting herself with voters last September, and Sununu’s relatively slow start has contributed to the Republicans’ nervousness about his campaign. Sununu only put together his campaign team in April — the latest of any candidate in a top-tier Senate race.

Cullen acknowledged that he has heard from Republican activists who are worried about Sununu’s campaign.

“Those people are wrong,” Cullen said.

When asked why some of his Republican colleagues are insinuating that he might not have the fire in the belly that spurred his 2002 primary bid, Sununu said that was “absolutely” not the case.

“None of my colleagues in the Senate … saw me on the campaign trail in 2002,” Sununu said. “We’ve got great organization. Listen, [in the first weekend of this month], we did 15 or 16 different events. My opponent did one or two. The weekend before, it was probably very similar. In terms of the kind of events, the reception, the organization, the response — I feel very, very confident that we’ve got the focus and the enthusiasm and the team to win.”

When Sununu was asked to discuss his strategy against Shaheen for this cycle, he firmly declined. “I certainly wouldn’t share with you,” he said. “Why would I lay out, why would any candidate lay out the approach that they’re going to take, every detail of the approach that they’re going to take to the race?”

He was, however, not timid about criticizing his opponent’s record as governor — something Republican strategists have said they would do to close the gap.

“I think her service as governor demonstrated a real lack of leadership, failure to deal with the most important problem facing the state … education funding,” Sununu continued. “And as a result of her failed leadership, that issue is still a crisis in New Hampshire today. She raised spending to record levels, tried to give the state a sales tax, which would have devastated our economy. That’s a pretty weak record.”

Shaheen spokeswoman Kate Bedingfield defended Shaheen’s tenure as governor and charged that Sununu was trying to take attention away from his record in the Senate “voting for George Bush’s failed policy in Iraq and supporting Bush fiscal policies, which have exploded the deficit.”

“Jeanne Shaheen was a strong leader for New Hampshire who expanded access to kindergarten and health care for New Hampshire’s children, implemented the first state law to reduce the four pollutants that contribute to global warming, presented a balanced budget to the Legislature every term she was governor and kept the state’s tax burden the lowest in the nation,” Bedingfield said.

An analysis of public events supplied by the respective campaigns of Sununu and Shaheen for the two weekends of April 26-27 and May 3-4 showed the incumbent bested Shaheen in the number of events when the tally includes official appearances, rather than just campaign stops. During those two weekends, Sununu’s staff listed 20 public appearances that the Senator made in New Hampshire, whereas Shaheen had about 10 public events over the entire past two weeks.

But of Sununu’s 20 in-state events, two were political in nature, such as a county Republican Party dinner. The remaining 18 were considered by Sununu’s office to be part of his official duties.

“He’s not publicizing his appearances as much as he usually does,” said one Republican official. “His travel has been a lot more quiet than it has usually been.”

The Republican, who declined to be named, suggested that publicizing Sununu’s weekend schedule might only invite trouble from Democratic activists who are tracking the incumbent.

“I think a lot of that disconnect is that they’re just not getting the press releases out there,” said the official. “It could be that he’s just more quiet, which could be feeding that rumor that he’s just not started.”

Jack Heath, a conservative radio host and GOP consultant who came within 1,000 votes of defeating Sununu in the seven-way GOP House primary in 1996, said Sununu’s perceived slow start may have something to do with the fact that the Senator takes on a lot of his campaign’s tasks himself.

“His engineering background is something not to be taken for granted,” Heath said. “He’ll engineer his own re-election. He’s not going to have a boatload of consultants doing his race.”

Online fundraising records show Sununu has not yet spent much on anything, let alone consultants. Through March 31, Sununu’s campaign had spent $595,100 of the $4.17 million he has raised so far this cycle — or a burn rate of about 15 percent. Shaheen had spent $725,600 of the $2.56 million she’s raised since she got into the race last September — a burn rate of about 28 percent.

Heath said Sununu never has a large campaign operation, in part because he runs much of it himself by relying on a few key individuals. Paul Collins, Sununu’s Capitol Hill chief of staff who is taking over the campaign, has been with the Senator for every one of his campaigns since 1996. Collins’ deputy and the campaign communications director were also on the 2002 campaign.

“His style of campaigning, I don’t know if there’s a U.S. Senator who’s as hands-on as him with his own re-election,” Heath said.