Leading national tea party groups and figures have gone all in for Republican Ben Sasse in the Nebraska Senate race, a high-stakes gambit that could either blunt or bolster their momentum heading into the heart of the 2014 primary season.

Republican U.S. Senate candidate Ben Sasse, left, former Alaska governor Sarah Palin, Texas Sen. Ted Cruz, Sharon Lee and Utah Sen. Mike Lee, stand together on the platform at Buffalo Bill State Historical Park in North Platte, Neb., at an April 25  rally for Sasse's campaign. (Job Vigil, The Telegraph/AP)

With less than two weeks to go until the Republican primary, Sasse has appeared to have moved to the head of a multi-candidate pack featuring two other major hopefuls. There's a lot resting on the next 10 days not only for Sasse, but also for the likes of the Club for Growth, Senate Conservatives Fund, Sen. Ted Cruz (R-Tex.) and Sarah Palin, who have all joined Sasse in one of the most intense primary campaigns of 2014.

Sasse, the president of Midland University, may represent the best chance for the national tea party movement to claim victory in a contested Senate primary this year. While Republican senators have been swarmed by primary challengers, most have fizzled amid intense scrutiny and a robust attempt by the establishment to define them early as outside the mainstream candidates. The open race in Nebraska presents an opportunity for the tea party to claim an early win against that backdrop.

Sasse is trying to get past former treasurer Shane Osborn (R), a more establishment-friendly figure who has been bludgeoned by Sasse's tea party allies on the airwaves, clearing the way for Sasse to run a positive air campaign. The two are also competing against Sid Dinsdale, a wealthy bank executive who has emerged as a threat to both candidates down the stretch.

The momentum Sasse has picked up is reflected in the well-heeled advertising push he has planned for the final week. Sasse has reserved approximately  $111,000 for television ads on broadcast and cable -- more than double what Osborn, who has been flailing, has thrown down for the final leg.

But Dinsdale, who has been outspent on the airwaves so far, plans to make a big final push, too. Dinsdale campaign manager Beth Kramer said in an interview that the campaign will spend nearly $200,000 for the final week -- a sizable sum that could propel him ahead.

There are shades of the 2012 Nebraska Senate primary in this year's competition. In that race, Republicans Jon Bruning and Don Stenberg battered each other with attacks, clearing the way for now-Sen. Deb Fischer (R) to make a late surge. Fischer was boosted by a Palin endorsement and support from billionaire Joe Ricketts.

"Negative campaigning doesn't work in this election it didn't work in Deb Fischer's race," said Kramer.

But the Dinsdale-as-Fischer comparison doesn't work so neatly. Palin is on Sasse's side. So is tea party hero Cruz and his close ally, Sen. Mike Lee (R-Utah). The three stumped for Sasse last week.

Even Freedomworks, which initially backed Osborn, switched its support to Sasse, a sign his campaign was surging and worth a bandwagon jump, especially given his pull in the tea party.

Sasse recently scored the backing of the Nebraska Farm Bureau, a coveted endorsement in a state where the agricultural industry is huge.

"We feel like we are well-positioned for the last stretch run," said Sasse campaign manager Tyler Grassmeyer.

Osborn campaign manager Bill Novotny, meanwhile, said Osborn's retail campaigning will pay dividends.

"Nebraskans want to look their next senator in the eye," he said.

To say the race has been nasty and personal would be an understatement. Osborn is casting Sasse as soft on Obamacare in a television ad campaign that Sasse's campaign says takes his words out of context. In response, Sasse has launched a TV ad in which his daughters defend his opposition to the health-care law and say that they "always pray for the opposing candidates at breakfast."

The Club for Growth has taken aim in a TV ad at Osborn's tenure as treasurer, saying the state auditor found "mismanagement, waste and unreasonable spending." Meanwhile, Osborn's military record has come under criticism in an ad from the 60 Plus Association, a seniors group backing Sasse.

Dinsdale has not been immune to barbs. On Thursday, conservative blogger Erick Erickson, who backs Sasse, wrote a piece taking aim at Dinsdale's relatives' ties to groups that support abortion rights.

What happens in Nebraska on May 13 could set a tone for other primaries happening soon. A Sasse loss is the last thing tea party groups need heading into a stretch of primaries during the next eight weeks including contests in Kentucky, Mississippi and Kansas, where insurgent conservatives remain underdogs in their quests to defeat incumbent Republican senators.

It would also prompt a fresh round of questions about endorsement criteria. Sasse once supported Medicare Part D, for example, which the Club for growth adamantly opposes.

But a Sasse win could light a fire under the national tea party movement. Tea party groups will soon have another opportunity in an open Oklahoma race, where they have begun to coalesce around former state House speaker T.W. Shannon (R) in a contest looking more competitive for him.

"Our PAC gets involved in lots of races. Sometimes we win, sometimes we lose. In the end, the voters get to decide," said Club spokesman Barney Keller.

In this race, what Nebraska voters decide will reverberate far beyond the state's borders.