Nebraska Republicans on Tuesday were choosing a candidate to square off against Democrat Bob Kerrey, a former senator seeking another turn on Capitol Hill in one of the year's most hotly contested Senate races. 

The GOP primary fight illustrates a years-old split between the two wings of the GOP. State Attorney General Jon Bruning, backed by establishment Republicans, is trying to overcome a spirited challenge from state Sen. Deb Fischer, who has tea party support. State Treasurer Don Stenberg also was on the ballot. 

Elsewhere, Oregon was deciding whether to give its 25 presidential delegates to Mitt Romney, the all-but-certain GOP nominee. Nebraska Republicans also were weighing in on the GOP race though no delegates would be allotted in a vote that amounts to a beauty contest. The state's 32 delegates to the Republican National Convention later this year will be determined at the state convention on July 14. 

Romney was 171 delegates short of the 1,144 needed for the nomination and is on pace to get them before the month ends. He was spending the day in Iowa, a competitive general election battleground, delivering a speech on the economy as he looks to counter President Barack Obama on voters' top concern. 

Idaho voters also were picking nominees for state and congressional offices. 

But the biggest race Tuesday was Nebraska's GOP Senate primary. 

Democratic Sen. Ben Nelson, a two-term moderate, is retiring and both parties are eyeing his seat. Democrats want to keep it to maintain their Senate majority, while Republicans see an opportunity in their drive to win back control of the Senate. 

Democrats control the Senate 51-47, plus two independents who caucus the majority. But the outcome in November of several competitive Senate races could result in a power shift. 

Kerrey, who served Nebraska as governor and as a U.S. senator before leaving Congress in 2001 to become a university president in New York, reluctantly agreed to run again to help give Democrats a shot at holding a seat they've long controlled. 

Republicans in Washington turned to Bruning, who has been successful in statewide races. But in the final stretch of the Senate campaign, he has found that his nomination is hardly assured. 

Fischer, a rancher in rural Nebraska, has mounted a feisty campaign that in the past few weeks has attracted attention and endorsements from former Alaska Gov. Sarah Palin, Sen. Jim DeMint of South Carolina and other tea party darlings. She's also backed by an outside group, created by TD Ameritrade founder Joe Ricketts, that's running TV ads on her behalf. 

Stenberg, for his part, has argued that he is the only "genuine, life-long conservative" in the race.