MANCHESTER — Six months ago, veteran political operative Mike Biundo and his presidential candidate, Rick Santorum, were pretty much just a twosome, moving town-to-town in New Hampshire and Iowa, meeting anyone they could and asking for support for an underdog and under-the-radar campaign.

Now, on the eve of “Super Tuesday” Republican primaries in 10 states with Santorum challenging Mitt Romney, life has changed for the 43-year-old Biundo, who may be the first Granite Stater to run a national campaign.

“There are only five people right now who are running campaigns for people who could become President of the United States, so it's exciting,” Biundo said in a telephone interview from the road.

Some things have changed, but Biundo is still focusing on a political specialty honed in New Hampshire — building grassroots support.

“But now, we're traveling in caravans of SUVs, and the Secret Service is doing the driving,” he said. “It's been a fun ride.”

Not that Biundo expects the ride to end anytime soon. But he knows that Tuesday may be a big turning point for the GOP presidential nomination.

Biundo said the Santorum campaign is involved in all 10 states, but is focusing on Oklahoma, Ohio, Tennessee and Georgia.

Biundo has been involved in campaigns for 20 years now. But being the top guy in a truly national campaign?

“It's been a whirlwind,” he said. “It's been so exciting because we feel really good about where we are right now, as a campaign.”

New Hampshire has had national advisers and strategists for presidential campaigns before: David Carney for Rick Perry and George H.W. Bush, Michael Dennehy for John McCain; and Susan Casey for Gary Hart in 1984, among others.

But Biundo's role may be the biggest yet.

Those who have worked with him are not surprised.

“He is someone who understands retail politics, and retail politics is very powerful,” said Roger Wilkins, a friend who worked with Biundo on U.S. Rep. Frank Guinta's campaigns in 2005 and 2007 when Guinta was successfully running to become Manchester's mayor, and, in 2010, a congressman.

“He's worked very hard to get where he is and it's no surprise at all,” said Wilkins, now Guinta's district director.

“Whoever he works for, he gives 120 percent. This is a self-made guy. He has worked his way up, and you'd expect one's knowledge base would be quite rich when you are involved at every level of a campaign and in every level of campaigns, too.

“You can't diminish being a New Hampshire operative,” Wilkins said. “That gives you a unique opportunity to navigate all kinds of challenges and experiences.”

Biundo, born in Brooklyn and raised on Long Island, has been in New Hampshire since 1988, living in Nashua and, since 1999, in Manchester.

His involvement in campaigns dates back to the early 1990s, when he worked in former state Sen. Tom Stawasz's effort, then the congressional campaign of Mike Hammond in 1994.

He was involved in Pat Buchanan's presidential campaign in New Hampshire in 1992 and then headed Buchanan's primary-winning effort here in 1996.

Biundo was executive director of Gun Owners of New Hampshire from 1998 to 2000.

He directed Guinta's mayoral campaigns and managed long-shot Republican Jim Coburn's campaign against Gov. John Lynch in 2006.

Biundo stayed with Guinta when Guinta first considered running for governor, but ultimately ran for Congress in 2010.

He signed on with Santorum last year.

Last week, he recalled having “five or six people at events” in New Hampshire through most of 2011.

“It's been a whole lot different lately,” he said. “We're focusing on lots of states and lots of logistics and the process has been exciting, exhilarating. It's been a hard road but it's great where we are now. I think we have a really good shot at this nomination.”

Even while Santorum was low in polling last year, Biundo said, he “always talked about this being the ‘Little Engine That Could' campaign, that we would bide our time and keep putting the message out there and at some point we would be the conservative alternative to Mitt Romney. And it played out that way.”

Santorum had an upset win in the Iowa caucus but fared poorly in New Hampshire.

“We weren't ready to be a national campaign,” after Iowa, Biundo said. “We had to raise more money and put bodies in place. Romney had a head start, but we caught up quickly.”

Santorum moved up in the national spotlight after winning Colorado, Missouri and Minnesota on Feb. 7.

Overall, running a national campaign has “a lot of similarities” to running a mayoral, congressional campaign or statewide campaign, Biundo said.

“But the intensity is much higher of course. You wake up every day and it’s three or four days from election day,” he said. “It’s certainly an exhausting process. It doesn’t stop. You have to be thinking ahead.”

On a personal note, Biundo said he is holding up well, despite waking up in a different state most every morning.

“Sometimes,” he said, “it's hard to keep track of where I am.”

He said he has seen his family in Manchester only 10 days since Dec. 7 and only three days since the New Hampshire primary on Jan. 10.

“It's tough,” he said. “They are extremely supportive. My wife (Robin) has always been very involved in campaigns with me, so it's very different that we're apart.”

They have a 22-year-old son and an 18-year-old daughter.

“They know that when you get into this business, it's a dream to do what I'm doing at this level,” Biundo said.