BOISE - Idaho voters will head to the polls Tuesday to set the stage for the fall campaign season, picking candidates for congress, the governor's office and a seat on the state's highest court.

The results may also provide a snapshot of the mood of the Gem State's Republican electorate and the ability of tea party supporters and other more conservative voters to reshape the state's dominant party.

Tuesday's primary comes in the aftermath of primary elections in states where fed-up voters lifted tea party darling Rand Paul to the GOP Senate nomination in Kentucky and sent stern messages to incumbents in Utah, Pennsylvania and Arkansas.

But what does the ornery national mood mean for Idaho?

Can conservative, tea party backers in Idaho's 1st Congressional District muster enough support to lift state Rep. Raul Labrador to an upset over Iraq veteran Vaughn Ward, who used his significant fundraising lead to buy television ads to rail against big government and the federal deficit.

Are moderate Republicans in the statehouse at risk of getting knocked off by newcomers hoping to make the state more conservative than it already is?

"There may be a few incumbents who are vulnerable," said Jasper LiCalzi, professor of political economy at the College of Idaho. "But I don't see any real groundswell against incumbency.

"The tea party, libertarian, less government idea is nothing really new here. It's been here since the 1970s and has already made Idaho a conservative state. When you compare Idaho to the nation, I'd say everybody else is starting to get like Idaho," he said.

Like recent primaries without a presidential election at stake, Tuesday's voter turnout is projected at 26 percent, according to Secretary of State Ben Ysursa. Polls are open from 8 a.m. to 8 p.m. statewide.

The state's most contested race pits Labrador and Ward for the GOP nomination. The winner will square off in November against first-term Democrat Walt Minnick to represent Idaho's western half in the U.S. House.

In other key races, popular, veteran Republicans have drawn challenges this year from rivals who have tried to exploit support for government bailouts or tax hikes.

Republican Gov. Butch Otter is competing against five primary challengers, including veterinarian and former Rexburg elk rancher Rex Rammell and Ada County Commissioner Sharon Ullman.

Otter, who is seeking a second term, has been criticized by his rivals for trying to raise state gasoline taxes in 2009 to pay for upgrades to the state's highway system. The plan also put Otter at odds with leaders of his own party, who refused to deliver the votes a year ago to raise taxes during a deep recession.

But Otter may have won back enough conservatives this year by leading the charge to sue the federal government over President Obama's health care reforms.

"I think that earned him his credibility back with conservatives," LiCalzi said.

In eastern Idaho, six-term U.S. Rep. Mike Simpson faces a primary challenge from Republicans Chick Heileson of Iona and state Rep. Russ Mathews of Idaho Falls. Both rivals have criticized Simpson for his 2008 vote for the first TARP bill, which authorized spending $700 billion to buy toxic mortgage securities.

In statehouse races, there are 15 contested Senate races and 19 contested House races. Republicans hold a 28-7 advantage in the Senate, and a 52-18 advantage in the House.

Tuesday's results will determine the outcome of a race for a seat on the Idaho Supreme Court between incumbent justice Roger Burdick and challenger John Bradbury, a state judge from the 2nd District Court. It's the second time Bradbury has sought a seat on the high court. In 2008, he fell 276 votes short of beating incumbent Justice Joel Horton.

Voters will also determine a handful of other Republican primary races, including a U.S. Senate seat and the job of Lt. Governor. But those contests have drawn scant attention given the chances of a loss by the incumbent.

Republican Sen. Mike Crapo, seeking a third term, is heavily favored to win the nomination over Claude M. "Skip" Davis III.

Lt. Gov. Brad Little, who was appointed by Otter last year to replace Jim Risch, who won Idaho's other Senate seat in 2008, is being challenged by Joshua Blessinger of Boise and Steven Pankey, of Shoshone.