After helping elect dozens of lawmakers to Congress in 2010, the Tea Party movement's influence will be tested again in the coming weeks as it attempts to oust the two longest-serving Republicans in the U.S. Senate and shift the chamber to the political right.
Sens. Orrin Hatch of Utah and Richard Lugar of Indiana -- both of whom arrived in the Senate in 1977 -- are this year fighting off Republican primary challengers backed by the Tea Party and its allies, who hope to establish not just a Republican majority in the Senate, but a majority that tacks more closely to the Tea Party's fiscally conservative, limited-government philosophy.
"We need people now who realize this is not business as usual," said Sen. Jim DeMint, R-S.C., who worked to defeat incumbent Republican Sen. Arlen Specter of Pennsylvania in 2010, but who said he isn't working to unseat any of his colleagues this year. "We've got to change the direction of the Senate, and that's hard for the people who've been here awhile."
One Tea Party-affiliated group, FreedomWorks, spent hundreds of thousands of dollars on television advertisements aimed at defeating both Hatch and Lugar. And the Club for Growth, another group backing Tea Party candidates, is working to defeat moderate Republicans running for open Senate seats in Nebraska and Wisconsin.
Among the Club for Growth's targets is Senate candidate and former Wisconsin Gov. Tommy Thompson, whom the group accused of supporting "massive tax and spending increases" and backing President Obama's health care reforms.
The Tea Party and its allies helped Republicans expand their clout on Capitol Hill in 2010, but their successes are more limited so far this year.
Despite conservative attacks, Thompson leads the four-candidate field in Wisconsin's Republican primary, polls show. The candidate endorsed by the Club for Growth and backed by the Tea Party, Mark Neumann, is running third.
In Utah, Hatch is holding his own against former state Sen. Dan Liljenquist, a Tea Party favorite backed by FreedomWorks, the group that helped defeat Utah's other U.S. senator, Bob Bennett, in 2010, replacing him with more conservative Sen. Mike Lee. In caucuses earlier this month, Hatch captured a majority of the delegates needed to claim the nomination at the party's convention in April, his campaign said.
"There was a different attitude among voters out here this time," Hatch campaign manager Dave Hansen told The Washington Examiner. "I think there were more Republicans who may not identify with the Tea Party who got involved this time."
Conservatives' best chance of knocking off a moderate incumbent may be in Indiana, where Lugar clings to a 6-point lead over primary challenger Richard Mourdock. Though he's served as long as Hatch, Lugar's record is generally more moderate, allowing FreedomWorks and the Tea Party to draw a more striking contrast between the incumbent and challenger in ads that focus on Lugar's support for a Wall Street bailout.
University of Virginia political science professor Larry Sabato said the Tea Party may not match its 2010 success rate, but that doesn't mean it's less influential this year.
"It had such a big year in 2010 that it is tough to duplicate that," Sabato said. "Also, elected officials like Orrin Hatch got the message, and they adapted their positions and rhetoric to fit the mood of their party's electorate."