Tea party challengers made waves in 2010 and 2012 by launching primary bids against well-respected, better-financed Republicans in Congress.
It looks like the 2014 election cycle will be no different, with several of the GOP's most venerable lawmakers already facing fights from within their own party.
The latest came Tuesday, with Tennessee state Rep. Joe Carr announcing he'll mount a challenge to two-term incumbent Sen. Lamar Alexander, the state's former governor who also served as secretary of education under President George H.W. Bush.
Whereas Mr. Alexander has often been at the negotiating table seeking compromise — he was a key player in crafting the recent bipartisan deal to reduce student loan rates, for example — Mr. Carr is casting himself as reliable, committed conservative, in the vein of an aggressive class of freshman Republican senators such as Mike Lee of Utah, Ted Cruz of Texas and Rand Paul of Kentucky.
"Tennesseans are hungry for strong, principled, conservative leadership, so I am answering the call," Mr. Carr wrote in his announcement. He told a Tennessee talk show that he considered Mr. Alexander "the most liberal member of the delegation from Tennessee."
Mr. Alexander, who did not even have a primary challenger in his 2008 race, easily won a second term that year with 65 percent of the vote.
Mr. Carr's announcement comes a week after some 20 conservative and tea party groups across the state published an open letter calling on the senator to retire. "Quite honestly, your voting record shows that you do not represent the conservative values that we hold dear and the votes you have cast as senator are intolerable to us," the letter read in part.
While GOP leaders fear — and Democrats hope — the primary fights could weaken the winner for the general election in November 2014, Mr. Alexander isn't alone among GOP stalwarts fighting for the right to run for another term.
In Kentucky, Senate Minority Leader Mitch McConnell — who has served in the Senate since 1985 — is facing a primary fight from Louisville businessman Matt Bevin, who trails badly in recent polls but has attracted some tea party support. Kentucky Secretary of State Alison Lundergan Grimes, a Democrat, also has entered the race.
In Wyoming, Sen. Michael B. Enzi has been challenged by Liz Cheney, daughter of former Vice President Dick Cheney.
Sen. Lindsey Graham of South Carolina also faces a primary fight, with several Republicans eyeing the race.
Such battles have become commonplace in recent years, with some highly recognizable figures in the GOP seeing their political careers come to an end at the hands of a fellow Republican.
In 2012, for example, Sen. Richard Lugar's six-term stay representing Indiana in the Senate ended when he lost a primary fight to Richard Mourdock, who went on to lose the general election.
Mr. Alexander on Tuesday defended his record, citing his ability to get things done while remaining faithful to conservative ideas.
"Washington needs more, not fewer, conservatives who know how to govern," Mr. Alexander wrote in Tuesday's Tennessean newspaper. "Governing means listening, standing up for what you believe in and solving problems to get a result. I did that as governor. I'm doing that as senator. ... We've made speeches. But that's not enough. We need a result. We need to solve the problem."
Before deciding to run for Senate, Mr. Carr, a businessman from Murfreesboro, planned to challenge incumbent Rep. Scott DesJarlais in Tennessee's 4th congressional district and had already begun to assemble a campaign machine for that race.
His decision to instead seek a Senate seat has cost him his top campaign strategist, Chip Saltsman, who resigned shortly after Mr. Carr made his announcement.
"I must resign from your campaign. I signed up to help you run for Congress, not the Senate," Mr. Saltsman wrote in a letter to Mr. Carr.
"I have been a longtime supporter of Sen. Alexander for many reasons, and I will continue to be a strong supporter," he continued. "It is because of Lamar Alexander that people like you have the honor of serving in the majority of the state legislature. ... I am honored to support Lamar Alexander for reelection."
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