BRENTWOOD, N.H. (AP) — Rick Santorum is counting on momentum — and perhaps help from outside groups — to carry him to victory in New Hampshire and beyond.

He has little choice.

The little-known Republican presidential candidate doesn’t have much of a staff in most states. He doesn’t have the kind of money his competitors have. And he doesn’t have much time to fix those deficiencies. New Hampshire’s primary is six days away, and the race quickly turns to South Carolina, Florida and other states where candidates historically need big organizations and big bank accounts to prevail.

“My name is Rick Santorum, and I am the only authentic, passionate conservative who can unite the GOP,” Santorum wrote in a fundraising missive sent as Iowa caucus votes were being tallied in a race he barely lost. “I need an URGENT contribution of at least $35 today to unite conservative voters and win the Republican nomination.”

There were indications the plea may have worked: Santorum has already seen a surge in online donations, which crippled his campaign’s website shortly after the Iowa results were announced. And campaign manager Mike Biundo has said the campaign’s fundraising pace has tripled over the last week.

Even so, Santorum, who nearly won the caucuses after devoting virtually all his time and resources to Iowa, has significant hurdles to climb if he hopes to challenge chief rival Mitt Romney for the party nod.

The former Pennsylvania senator has struggled in recent months to afford campaign basics, such as airfare and rental cars. He’s been largely ignored in the debates. And his lengthy record in the Senate, which includes controversial statements about gay rights, among other social issues, has yet to be fully scrutinized, meaning attacks are likely.

“Santorum still has a lot to prove,” said cultural conservative Kevin Smith, a candidate for New Hampshire governor who recalled presidential campaigns past when “one candidate does very well in Iowa and then fizzles after that,”

Santorum is looking to avoid that fate.

Mindful of the challenges, campaign aides stayed out of sight most of Wednesday as the candidate and his small team flew to New Hampshire for an evening rally.

Santorum previewed his likely pitch in the email, saying the time has come for divided conservative voters — as well as tea party activists and so-called values voters — to embrace him. “We can either unite now behind one candidate and have a conservative standard bearer in 2012, or have the GOP establishment choose another moderate Republican who will have a difficult time defeating Barack Obama in November,” Santorum wrote. It was a clear slap at Romney and an indication that he wouldn’t shirk from assailing his chief opponent as he looks to emerge as the consensus conservative candidate.

Santorum has vowed to compete in New Hampshire — where Romney has a significant advantage in polls — despite clear vulnerabilities, including that he’s barely registered in surveys here this year. The electorate here also is far less conservative on social issues, which is Santorum’s strength.

Perhaps his biggest weakness is that he has virtually no campaign presence on the ground in any other early voting state. In contrast, Romney and Texas Rep. Ron Paul both have staff and organizations in several states.

That takes money — and Santorum hasn’t had it all year. He reported less than $200,000 in his campaign account at the end of the September, the most recent figure publicly available. Romney, by contrast, finished the quarter with $14.7 million.

Biundo said Santorum was trying to add staff. But he also cautioned that giant payrolls don’t guarantee wins.

Romney himself proved that. Four years ago, he had 52 aides in Iowa and still came up short to Mike Huckabee’s shoestring operation. Huckabee, however, would fade as the contest moved beyond Iowa.

“We are going to hire more people, but we are not going to spend millions and millions of dollars like these other campaigns. We feel that we can do it a little bit different,” Biundo said. “We can do a lot of grassroots because we have the support out there, but we will be expanding our staff.”

A so-called super PAC dedicated to helping Santorum could be a key to his success, or lack thereof, going forward.

The group, Red, White and Blue, spent money in Iowa in the final weeks of Santorum’s campaign. It can accept unlimited donations and spend freely.

Other outside groups may help as well.

The leader of the political arm of Catholic Vote distributed a message to supporters Wednesday suggesting they take a second look at Santorum, a Catholic.

“I’ll be honest, I wanted CatholicVote to endorse him months ago. But any endorsement must involve the heart and the brain,” wrote the organization’s president, Brian Burch. “And until the last two weeks, it wasn’t clear whether Santorum would get the traction he needed to compete. Last night he put these doubts firmly to rest.”

Yet with Santorum’s rise, his record will earn him a second look. Already, his track record was called into question, including his endorsement of Sen. Arlen Specter, the Republican who later bolted his party to become a Democrat. And Republicans here question his electability, particularly compared to Romney.

But it’s the fragileness of his campaign operation in general that’s giving some people pause as they look for a winning candidate to support.

“A huge concern” was how New Hampshire state Rep. Pete Silva, a Rick Perry backer who’s considering alternatives, put it.

“Santorum has no ground game at all. He’s not doing squat here. He’s nothing in the polls,” Silva said, adding that he’d consider voting for him if Perry drops out. “It would be more a ceremonial thing. Who’s going to beat Romney now?”