Washington (CNN) -- With their eyes on winning control of the U.S. Senate in November, Republicans will be looking Tuesday to the primary for Nebraska's open seat, where the yet-to-be-decided Republican candidate is already favored over the former senator expected to win the Democratic nod.
Sen. Ben Nelson, a Democrat, is retiring, leaving an open race rated by two prominent independent political handicappers as "likely Republican" and "Republican favored."
The likely Democratic candidate, former Sen. Bob Kerrey, did not seek a third term in the 2000 election, and is expected to face either state Attorney General and frontrunner John Bruning, state legislator Deb Fischer, or state treasurer Don Stenberg.
Voters in Idaho and Oregon will also cast ballots for U.S. House and state-level races.
Rep. Suzanne Bonamici is the only Democrat on the ballot in Oregon's first district, a seat she assumed in February after Rep. David Wu resigned amid an ethics investigation involving an allegation of a sexual encounter with the daughter of a donor to his campaign.
The Nebraska primary has drawn in national figures such as former Alaska Gov. Sarah Palin, who endorsed Fischer a week ago, and the tea party group FreedomWorks, which in September said it would back Stenbebrrg.
All three are backed by anti-abortion organizations and tout their Second Amendment credentials.
Bruning touts his support for and action on a lawsuit against the health reform law, as well as his opposition to abortion and current levels of federal spending.
"The federal government spends too much, taxes too much, regulates too much, and listens too little," his campaign website reads.
His prominent endorsements include Arkansas Gov. Mike Huckabee, the U.S. Chamber of Commerce, and the Tea Party Express.
Bruning has outraised his GOP rivals, raking in nearly $2.9 million this cycle.
Stenberg won his party's nomination once before, when he faced Nelson for the open seat in 2000, and also ran in 1996 and 2006.
In addition to the backing of FreedomWorks, Sen. Jim DeMint's Senate Conservative Fund has aired television spots for Stenberg which criticize his rival Bruning, who Stenberg says is not a genuine conservative.
He has been endorsed by the Family Research Council PAC, the Club for Growth, conservative talk show host Mark Levin, conservative blogger and CNN Political Contributor Eric Erickson, and several potential future senate colleagues, including Rand Paul and Mike Lee.
Despite the endorsements he has raised approximately $680,000.
Fischer points to her experience as a state legislator, where she and her colleagues have balanced the state budget while providing tax relief.
Her five step plan for federal government reform includes a balanced budget amendment to the U.S. Constitution and repeal of the health reform law, the Dodd-Frank banking law, and the No Child Left Behind education statute.
She also proposes greater Congressional oversight, an audit of the Federal Reserve, and downsizing or elimination of some government agencies.
While reliable polling in the state has been scarce, two independent political analysis show Nebraska switching hands from Democrats to Republicans.
The Cook Political Report lists the race as "likely" a Republican pickup -- which falls between "solid" and "lean" -- while the Rothenberg Political Report calls it "Republican favored," one step below a safe seat but three steps above a toss-up.
Democrats are defending or facing a retirement in 23 of the 33 Senate seats up for election this year. Of the 10 open seats, seven are held by Democrats and three by Republicans.
The GOP would need to pick up four seats to gain a simple majority in the body.
While the GOP candidates have exchanged elbows through a series of television advertisements, they have found time to beat up on Kerrey and have been joined by national operations, such as the American Crossroads committee founded by Karl Rove.
Within days of Kerrey's decision to enter the race -- he initially said he would not run, then two weeks later, announced he would -- Bruning was on the air with an ad questioning the former senator's residency. After stepping down from the Senate in 2001, Kerrey lived and worked in New York.
Kerrey is a "New York liberal," Bruning's ad went, while American Crossroads said, "A decade in Greenwich Village changed Bob Kerrey."
The group also seized on his reluctance to enter the race, claiming in a radio ad that Kerry "cut his own secret deal with Democratic leaders in Washington, a deal so secret Kerrey won't talk about what promises were made."
The state Republican Party even filed an official challenge of his residency with the Secretary of State's office.
His campaign manager, Paul Johnson, told CNN in March that the residency attacks were "insulting to Nebraskans" and that Bob is "a fiscal conservative" concerned with national debt and budget deficit.
Other attacks have sought to tie Kerrey to outgoing Nelson -- who provided the 60th vote for Democrats to pass the health care overhaul.
He agreed to support the bill after negotiating a compromise, which came to be known as the "Cornhusker Kickback," which would have modified federal abortion funding regulations and saved the state approximately $100 million on Medicare costs over a decade.
But after Republican protests at home and nationwide, he had the provision removed.
Like others in the upper chamber who are retiring willingly or unwillingly this year, Nelson is known for crossing the aisle.
While this open seat has taken a backseat in prominence to the race for others -- such as last week's primary defeat of Republican incumbent Sen. Richard Lugar in Indiana -- this state has a front seat to an issue splitting the two parties this year.
The controversial Keystone XL oil pipeline, generally favored by Republicans and opposed by Democrats, was to stretch from Canadian oil sands to the Gulf Coast, bisecting Nebraska. But environmentalists worried about polluting the Ogallala Aquifer, which supplies most of the state with drinking water.
Nelson easily won a second term in 2006, but as it became clear that Republicans considered his seat in play this cycle, Nelson made a December announcement that he would not seek a third term.
"Simply put: It is time to move on," Nelson said at the time.
Nebraska is expected to be anything but tranquil as the race heats up this summer.
Don Walton, a political writer with the Lincoln Journal Star, had a simple warning in his pre-election Sunday column: "buckle up."
CNN's Paul Steinhauser, Gabriella Schwarz, and Kevin Liptak contributed to this report.