RESEARCH TRIANGLE PARK, N.C. — In a chilly television studio, out of sight from the camera, Thom Tillis is waving a red card that says "rebuttal." A Republican rival for the U.S. Senate has just compared him to Sens. Lindsey Graham and John McCain — bêtes noires of the right.

"Being conservative is something you do, not just say," Tillis says as the camera returns.

The speaker of the North Carolina House of Representatives, facing a strong tea party challenge, boasts of leading a "conservative revolution" that includes strict voter ID laws and rejecting an expansion of Medicaid.

Tillis' defense reflects North Carolina's status as the latest battleground in the struggle over the GOP's identity. After five years of being pushed hard right by grass roots activists, the establishment is pushing back.

It is confronting a tea party suffering from waning enthusiasm, controversial candidates and bad publicity, early signs of a shift in the movement that rocked politics and left a mark, from deep budget cuts to immigration and last fall's government shutdown.

A string of tea party hopefuls, from Texas to Tennessee, South Carolina to Kentucky, have failed to gain traction this year, slowed by their own shortcomings or overpowered by the orchestrated effort to prevent the next nomination of candidates like Christine O'Donnell, Sharron Angle or Richard Mourdock.

The GOP needs to pick up six seats nationally to take control of the Senate and North Carolina is the first in a monthlong series of contests in which the intraparty fight will play out.

A recent poll shows Tillis breaking the 40 percent mark to avoid a runoff in Tuesday's primary. A Tillis win — and a showdown with vulnerable Democratic Sen. Kay Hagan — would improve the GOP's chances.

"I do believe the other candidates represent a serious risk of being able to do our part to get the Senate to a majority," Tillis, 53, said in an interview.

At the same time, the necessity for Tillis to play up conservative credentials shows that while the tea party may be down, its influence remains.

Tillis' toughest competitor is Greg Brannon, an obstetrician, father of seven and political novice who has been endorsed by tea party icons Sens. Rand Paul and Mike Lee. Brannon, a slight man with focused eyes and swept-up, graying hair, seems to mention the Constitution in every other breath. He likes to call Tillis, who has the look of a banker and the steadiness of a political pro, a "moderate."

But Brannon's uncompromising campaign lacks the organization and finances of Tillis, who has received support from some of the leading Republican forces trying to stifle the tea party.

Paul plans to campaign for Brannon today in Charlotte. Former Florida Gov. Jeb Bush endorsed Tillis last week, solidifying the tea party versus establishment storyline.

"I don't disagree with anything the tea party stands for, but it doesn't have support to win elections. I want to win," said Sonny Scott, 66, a Tillis supporter. His wife, Alice, attended tea party meetings early on but lost interest as the group strayed from economic issues to social ones, which she said aided Democrats with women voters.

An urgent message on the website for a tea party group in Randolph County, west of Raleigh, captures the mood:

"It seems that many have returned to the complacency and apathy that led us to requiring a movement like the TEA Party in the first place. We're losing the momentum that we once had and, should this continue, we'll not only lose the ground gained just a short 3 years ago, but soon become a muted voice of the people."

Terry Locke, 46, a graphic artist who wrote the note, said that standard Republicans "who were jazzed up about the tea party a couple years ago aren't as jazzed up" and no longer show up for meetings. Barack Obama's re-election also drained energy from a movement ignited in 2009 in opposition to his policies and rising national debt.

"The tea party is fighting a war on two fronts now, not just the left," said Locke, whose group has hosted Brannon. "The Republicans as a party like to control the message and the candidates." He said the GOP has been engaged in a whisper campaign about Brannon. "They're trying to drop the bug of doubt."

Bob Youngblood, chairman of the group, predicted energy would return as the November elections approach, but he fears a successful establishment push-back. "If that happens, we're toast," he said. "There are too many like John McCain that like to extend their hand across the aisle. Illegal immigration will be a fact."

Other tea party leaders in North Carolina reported a similar dropoff in energy. The Henderson County Tea Party website currently advertises its next meeting on Jan. 15, 2013. "The steam's out of the locomotive," said Ron Kauffman, ex-chairman of the group.

"You saw people vote for tea party candidates out of frustration. They weren't really tea party supporters but they were sending a message," said Jennifer Duffy, who analyzes Senate races for the nonpartisan Cook Political Report. "In some cases they woke up the next morning and said, 'Uh-oh, what did we do?' Those people aren't casting protest votes so much anymore."

Still, writing the tea party's obituary is premature at best.

GOP primaries have become a sprint to the right and a test of one's unwillingness to compromise in Washington — the hard-line that Sen. Ted Cruz of Texas rode into last fall's government shutdown. Immigration reform, which the national GOP wants to tackle to address abysmal performance among Hispanics and Asians, is stymied in a House taken over by the tea party wave of 2010.

"Tea party candidates are going to lose the nominations but win the policy stands," said Theda Skocpol, a sociologist and political scientist at Harvard University and co-author of The Tea Party and the Remaking of Republican Conservatism. "The Republican Party remains enthralled to these people."

A number of Republican Senate incumbents up for re-election this year have withstood tea party challenges but mostly by moving to the right on issues. At the annual Conservative Political Action Conference in March, Sen. Mitch McConnell of Kentucky, the epitome of the party elite and a backer of Tillis, walked on stage pumping a rifle in the air. For his part, Tillis has played up opposition to abortion and gay marriage.

There is little disagreement on the issues among the Republican candidates here. But Tillis and his supporters are making an argument that he is the most electable against Hagan, who defeated incumbent Sen. Elizabeth Dole amid the Obama wave in 2008. During a debate, Tillis repeatedly referred to Hagan, calling her "my opponent."

"We squandered collectively five Senate seats over the last two cycles because we had fundamentally unelectable candidates," said Rob Engstrom, national political director at the U.S. Chamber of Commerce, which last week launched ads supporting Tillis and several other Senate candidates.

Tillis has also gotten at least $1.5 million in TV ad support from American Crossroads, a Super PAC overseen by Karl Rove, who has vowed to lift up more mainstream candidates.

On the other side are national groups that helped build the tea party, including FreedomWorks, which has provided organizational support to Brannon. "They think they can dump a lot of money in the race and lift up a flawed candidate," said Matt Kibbe, the group's president. "We're organizing on the ground."

He argued that the tea party is not losing momentum but evolving.

"Anyone looking for a million people on the (National) Mall isn't going to find it. You're going to have to look at the local get-out-the-vote efforts and it's a very decentralized, granular movement," he said. "I think that's a sign of maturity."

Kibbe, though, has added steps to the group's endorsement process to weed out weaker candidates. Though social issues are not a priority for FreedomWorks, it has asked candidates for their views on abortion. "I want to know how candidates are able to communicate their positions," he said.

To remain vibrant, the tea party will have to recruit new members. Chris Wilson, 37 and a Republican, seems ideal. He works at a Cracker Barrel in Henderson, a small town north of Raleigh, and said he's gotten more conservative in the past decade. He loathes the health care law, which he says is costing him more money.

"I just watch this country and to tell you the truth, it scares me, just the way it's going." But Wilson said he's turned off by the tea party.

"The strong Republican front is now divided. When Sarah Palin and all them started it up, the idea was great. Republicans needed a kick in the butt," he said. "But I'm glad to see the tea party fading. It's just too conservative. The government shutdown was ridiculous."

Contact Alex Leary at leary@tampabay.com.