A trio of Republican candidates in Alaska is battling to the finish for the shot to take on one of this year’s most vulnerable Senate Democrats – but polls indicate the two underdogs in the race will need a late surge to topple the front-runner, former state attorney general Dan Sullivan.

The three candidates are facing off in Tuesday’s Senate GOP primary; the winner will face Democratic Sen. Mark Begich in the fall.

Sullivan, who is also a Marine reservist and former commissioner in the Department of Natural Resources, is leading the small pack in the eleventh hour. He’s got the most money -- having raised $4 million with $204,000 still in the bank -- and he’s leading in the few major polls conducted over the summer.

But his two competitors are nevertheless well-known: Lt. Gov. Mead Treadwell and Tea Party favorite Joe Miller, whose campaign got a shot in the arm on Friday when ex-governor Sarah Palin endorsed him, saying he has the “guts, wisdom, experience and optimism to fight for what is right.”

One of the most recent polls, taken at the beginning of the month by Public Policy Polling, found Sullivan leading with 35 percent, to Treadwell’s 29 percent and Miller’s 20 percent.

“I think that it’s Dan Sullivan’s [primary] to lose,” said Alaska politics blogger Amanda Coyne, who’s been covering the race, particularly the polling and media campaigns. She recently posted the results of an internal poll at the Sullivan campaign that gauged Sullivan ahead by 17 points.

Another indicator is Sullivan’s fundraising support, particularly from heavy-hitters in the party -- Sullivan got a big infusion of more than $300,000 from Karl Rove’s super PAC American Crossroads, and has the backing from Washington movers like the Club for Growth. Meanwhile, Begich has already gone out of his way to attack Sullivan exclusively, signaling that his own internal polling is showing Sullivan as the man to beat if he has any chance of keeping his seat in November.

But the race is tight enough that nothing is inevitable, said James Muller, professor of political science at the University of Alaska in Anchorage.

“Most of the polls I’ve seen show the race is tightening,” he told FoxNews.com. “The big question right now is how good turnout will be,” as Alaskans tend to be away from their polling stations in the summer, a time when absentee ballots really can make a difference.

There are fewer than 500,000 registered voters in the state, and far fewer vote in a party primary.

Treadwell, however, has been a capable opponent, brandishing his conservative bona-fides and long ties to Alaska politics and its oil-and-energy industry, say election observers. He served under Gov. Wally Hickel in the early 1990s as deputy commissioner of Alaska's Department of Environmental Conservation, and then later as chair of the U.S. Arctic Research Commission, to which he was first appointed by President George W. Bush, from 2006 to 2010. He was sworn in as Republican Gov. Sean Parnell’s lieutenant in 2010.

“I do think Mead started out this campaign knowing more people than Dan,” said Muller, who calls both men “highly qualified, talented, intelligent people.” Not to be deterred by the polling, Treadwell has been stepping up the attacks on Sullivan in recent weeks, saying he’s not ready for prime time. He’s also called him an outsider from Ohio (Sullivan settled in Alaska in 1997), who has spent little time living or working in Alaska, due to multiple tours overseas with the Marines and a stint as assistant secretary of state for counterterrorism under Bush.

Sullivan has attacked, too, sending out fliers saying Treadwell, who was born and raised in Connecticut and settled in Alaska in 1978, has ties to a company that took federal stimulus funds that he has publicly criticized.

When reached by FoxNews.com, Treadwell’s staff said he was nevertheless bolstered from the support he’s receiving on the campaign trail. “We’re at a fast gallop,” Treadwell said in a statement, noting that he just won (among Republicans) the Tanana Valley State Fair Straw Poll sponsored by the League of Women Voters. Begich won overall.

That, and other indicators, “probably explains why our opponents are scrambling with their attack ads,” he said. “Bottom line, I am deeply moved by the overwhelming support we’re receiving from Alaskans from all over the Last Frontier … our focus on issues important to Alaska is resonating."

And what about Miller? He appears to be the wild card, but not as wild as he might have been. Miller burst on the scene in 2010 when, as a Tea Party favorite, he beat Republican Sen. Lisa Murkowski for the GOP nomination for U.S. Senate. But she got on the ballot anyway, as a write-in candidate, and won.

Miller was hurt before that race was over. Between allegations that his private security team tied up and detained a local journalist, and a resurfaced scandal in which he used government computers to manipulate a party leadership election and then lied about it, his credibility took a hit.

“I think Joe Miller had his shot,” said Nathan Gonzales, deputy director of Washington-based Rothenberg Political Report, which puts the Alaska race in the top five of the most vulnerable Democratic senate seats up for grabs.

“He was able to generate his excitement early when the Tea Party was getting ramped up,” Gonzales told FoxNews.com. “But he picked up negatives, negatives among Republicans, along the way.”

Still, says Coyne, she considers him “gaining some traction” from some effective attacks on his opponents on issues like immigration. “He’s by far the best debater and the most natural politician among the three.” Though Miller, a former government attorney and combat veteran who graduated from Yale and West Point, has largely said he would not run as a third party or write-in candidate if he loses Tuesday, “you never know,” Coyne added.

Whoever wins has a decent shot at beating Begich, but it is clear from the money the incumbent senator is raising -- $8.3 million, with $2 million still in the bank – and the utilization of paid Democratic field organizers registering people in Alaska’s far-flung rural villages, that he is going to be putting up a fight, said Gonzales.

“Whoever wins Tuesday has to unify the Republican Party and raise a ridiculous amount of money,” he said.

Muller said the Republican Party should be happy with the outcome either way, as the two leaders -- Treadwell and Sullivan -- are capable of mounting strong campaigns against Begich. “It’s kind of an embarrassment of riches for people who favor politics on that side.”