IDAHO FALLS, Idaho -- Ground zero in the Republican Party's fight to define its future is on the opposite side of the country from Washington, amid snow-covered mountains and the Snake River canyon, in a House race that pits the business community against the Tea Party.
It's in Idaho's 2nd District where Rep. Mike Simpson, an Appropriations Committee chairman and ally of House Speaker John Boehner, is fighting for re-election against fellow Republican Bryan Smith, a lawyer and political novice aligned with the limited-government movement.
Multiple Tea Party groups back Mr. Smith, who says Mr. Simpson doesn't reflect the district's "conservative values." The threat to Mr. Simpson has awakened national and local business groups and Idaho companies with little or no history of getting involved in primary contests, and is a top priority for the U.S. Chamber of Commerce.
"Extremists haven't proven themselves to be very sympathetic to the needs of business," said Alex LaBeau, president of the Idaho Association of Commerce & Industry. "It is more populism than conservatism."
The association formed a supercommittee for political action, which allows it to raise and spend unlimited sums on campaign messages, late last year after learning of Mr. Simpson's challenger.
The outcome could change how the House operates in 2015. Last year's partial government shutdown was led by the Tea Party caucus in the House, and business groups were stunned when some of those members resisted raising the government's debt ceiling while discounting a default's economic impact.
A shift in the number of Tea Party allies could determine Mr. Boehner's flexibility in avoiding such faceoffs and passing other business priorities, including infrastructure spending.
"Business entities in Idaho have a long history with Congressman Simpson," said Mike Reynoldson, the Idaho government affairs manager for Boise-based Micron Technology Inc., the largest U.S. maker of memory chips and the employer of almost 6,000 people in the state. "In this race in particular, we saw a number of out-of-state interests were recruiting candidates and raising money and decided we needed an Idaho- based solution to offset the noise."
Similar dynamics are playing out in U.S. Senate races, where seven of the 12 Republican incumbents up for re-election this year face primary challengers, most aligned with the Tea Party. These showdowns also may act as a proxy for the party's direction heading into the 2016 presidential campaign season.
In the House, races pitting business against the Tea Party are also developing in Michigan, Pennsylvania and elsewhere.
Mr. Simpson's Idaho district covers most of the state's southern half and is home to a robust potato crop and one of the nation's most concentrated Mormon populations.
It's also one of the most heavily Republican districts. Mitt Romney, who has endorsed Mr. Simpson, won 64.5 percent of the vote in the 2012 presidential election. The victor of the May 20 primary will almost certainly win the seat, which explains the early entry by advocates on both sides.
The U.S. Chamber, the nation's largest business-lobbying group and a traditional Republican supporter, has already run ads boosting Mr. Simpson. Defending Main Street, a super-PAC affiliated with the Republican Main Street Partnership and its call for policy "pragmatism," plans to spend as much as $1 million to help the incumbent even though the group would rather focus on competitive open seats.
"We have to go in and defend him," said Sarah Chamberlain, the partnership's chief operating officer. "That will be our No. 1 seat."
Tea Party allies are also making the race a testing ground. The Club for Growth, a Washington-based group favoring spending cuts, is backing Mr. Smith, as are the Washington-based small-government advocates FreedomWorks and the Madison Project.
Mr. Smith, 51, dismissed the importance of the business groups backing Mr. Simpson, 63, and said he'll have enough campaign money and support from outside groups to be competitive.
"Congressman Simpson's values do not reflect the values of the district," he said during an interview at his Idaho Falls law office. "This is a very conservative district and Congressman Simpson has a moderate voting record."
Mr. Simpson is out of step with the rest of the state's four-person delegation, Mr. Smith said.
"He's the odd man out on many of these important votes," he said, citing Mr. Simpson's votes on increasing the federal debt ceiling and the $1.1 trillion funding bill, which passed the Republican-led House earlier this month on a bipartisan vote of 359-67.