(CNN) - The Republican primary in Tennessee on Thursday is the tea party's last chance - albeit a distant one - to beat an establishment incumbent this election year.
Longtime GOP Sen. Lamar Alexander is defending his seat against state Rep. Joe Carr.
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Despite picking up endorsements from conservative powerhouse Sarah Palin and the Tea Party Nation, it's an uphill battle for Carr, who trails the two-term senator in the polls.
Not to mention, Alexander handily won his last election with 65% of the vote and has raised significantly more campaign cash.
Carr pegs campaign on immigration
Carr has staked his campaign largely on Alexander's stance on immigration, slamming the two-term senator's vote last year for the Senate's comprehensive immigration reform bill - legislation that ultimately stalled in the House.
Alexander was among 14 GOP senators who voted for the comprehensive bill that Carr contends amounts to amnesty for undocumented immigrants.
The issue of immigration is back into the national spotlight as a surge of unaccompanied minors from Central America are crossing the U.S.-Mexico border, flooding emergency facilities and igniting a debate in Washington over what to do with the latest influx of immigrants.
As Congress and the White House lock horns over the border crisis, Alexander, known as a lawmaker willing to work with Democrats to broker bipartisan deals, recently aligned himself with tea party star and Texas Sen. Ted Cruz on the issue.
Alexander's campaign hasn't been taking any chances from the beginning, running campaign ads as early as last July before he had any primary challengers.
Carr has also made a push for defunding Obamacare, as well as arguing Alexander is out of step with Tennessee voters.
The state representative was originally planning to challenge Republican Rep. Scott DesJarlais in Tennessee's 4th U.S. Congressional District, but dropped his bid in order to take on Alexander.
Tea party wins spark hope for Carr
Carr's campaign received a jolt of enthusiasm after little-known professor David Brat upset House Majority Leader Eric Cantor earlier this year in Virginia's GOP primary.
Then, longtime Sen. Thad Cochran of Mississippi was forced into a runoff against tea party challenger Chris McDaniel after initial primary results were too close to call. Cochran narrowly beat McDaniel in the runoff but the challenger's campaign is contesting those results.
"Make no mistake about it - the fight that Chris McDaniel started in Mississippi will continue here in Tennessee," Carr said after the Mississippi runoff.
But unlike McDaniel, polls indicate Carr's the distinct underdog to Alexander. And, aside from the ongoing vote battle in Mississippi and Brat's unexpected victory over Cantor, the establishment wing of the Republican Party has come away from this election cycle relatively unscathed.
Five other lesser known candidates are competing in Thursday's GOP contest in Tennessee, a factor Alexander benefits from as grassroots support is divided behind his leading challenger.
The winner of the Republican primary will go on to face one of four Democrats and a series of third party candidates in November's general election, though the seat is considered a safe bet for Republicans.
CNN's Ashley Killough and Paul Steinhauser contributed to this report.