The tea party movement celebrated its fifth anniversary this past week, but there’s been little to celebrate lately about the performance of some of the conservatives running under the tea party banner who have mounted primary challenges to half a dozen Senate Republicans.

In Texas, a poll by the University of Texas and the Texas Tribune showed Sen. John Cornyn running away from Rep. Steve Stockman, 62 percent to 16 percent. Their primary will be Tuesday. At this point, the challenge to the incumbent looks like a big fizzle — to no one’s surprise.

In Kentucky, businessman Matt Bevin, the tea party candidate challenging Senate Minority Leader Mitch McConnell, has been trying to square his praise for the Troubled Asset Relief Program (TARP) in late 2008 with claims that he would have opposed the TARP program — which McConnell supported — had he been in the Senate at the time.

In Kansas, Milton Wolf, a radiologist who is trying to unseat Sen. Pat Roberts, had to apologize this past week after the Topeka Capital-Journal reported that he had posted X-rays of gunshot wounds on his Facebook page a few years ago and then made jokes about them.

In Mississippi, state Sen. Chris McDaniel, who is trying to defeat Sen. Thad Cochran, has had a rocky time after recently telling Politico’s Alex Burns that he wasn’t sure whether he would have voted in Congress for Katrina relief funds after the 2005 storm devastated his state. “That’s not an easy vote to cast,” he told Burns.

The outcome of the challenges to these incumbent Republican senators (and two others in South Carolina and Tennessee who also face challenges) will be one measure of the balance of power inside a party divided between its establishment and insurgent wings.

The tea party movement continues to have a significant effect on the Republican Party, pro and con. Without its energy, it is questionable whether Republicans would have made such large gains in 2010. But after a series of misfires with tea party candidates who proved not ready for prime time in the past two elections, and because of the unhappiness over the tea party’s role in helping force the partial shutdown of the government last fall, the GOP establishment has decided to fight back.

The tea party challengers hope to tap into the grass-roots anger on the right against both Washington careerism and the party’s congressional leadership. At an earlier time, many of them would have scratched for resources to mount serious challenges. Today they can look for help from an array of outside conservative groups (some more effective than others) such as the Senate Conservatives Fund, the Club for Growth, FreedomWorks, the Madison Project, the Tea Party Patriots, Tea Party Nation or the Tea Party Express.

Establishment GOP leaders have tried to step carefully through their divided party. They are understandably skittish about antagonizing tea party activists, whose enthusiasm will be needed in the general election this fall, when the party tries to take control of the Senate from the Democrats. But they have been outspoken in their dislike for the outside groups for backing candidates challenging their incumbents. Establishment Republicans looking to reassert their power see these primary battles as one place to start.

“Winning speaks volumes,” said Brad Dayspring, communications director of the National Republican Senatorial Committee, an organization whose dual responsibilities are to defeat Democrats and protect GOP incumbents. “It’s as simple as that. Results matter. Candidates who run good campaigns matter. At the end of the day, in politics as in business, the proof is in the pudding.”

Asked what’s at stake for the tea party movement in these races, Russ Walker, national political director of FreedomWorks, said: “The insurgent limited-government movement really has succeeded, regardless of whether they win or lose these challenges, simply because these candidates are being challenged. It’s rare they get challenged, and it’s rare they have to come up and defend their records.”

“I know that the Republican establishment thinks that if they win a few races and defeat a few conservatives that the conservative movement is going to fold up its tent and go home,” said Matt Hoskins, executive director of the Senate Conservatives Fund (SCF). “That represents a fundamental misunderstanding of the conservative grass roots and what drives them. . . . I think that they’re more panicked about it than ever before and they’re more hostile than they’ve ever been before.”

At this point, these challengers appear to be running uphill. The major outside groups have not backed anyone in the Tennessee race against Sen. Lamar Alexander. In South Carolina, Sen. Lindsey O. Graham faces several primary challengers, but none has yet made serious headway. A recent poll showed Graham with 45 percent among GOP voters; not one of his opponents was in double digits.

In Kentucky, McConnell has to worry about both a primary contest and a serious general election challenge from Democratic Secretary of State Alison Lundergan Grimes.

FreedomWorks, the Senate Conservatives Fund and the Madison Project are among those backing Bevin. The Club for Growth has not endorsed.

The embarrassment over what Bevin had said about TARP earlier, when he was running an investment firm, has raised questions about how thoroughly the outside groups have vetted these challengers. When asked whether the SCF team knew about Bevin’s previous position on TARP, Hoskins said, “We knew Matt Bevin was opposed to the Wall Street bailout and that has not changed.” Walker of FreedomWorks said he wasn’t sure whether the group’s research team had known about the problem.

Of all of the incumbents with challenges, Cochran in Mississippi is seen as potentially the most vulnerable. Cochran is an old-school legislator who was elected to the House in 1972 and to the Senate in ’78. In an interview with a Mississippi television station last month, he admitted that the tea party was something that “I really don’t know a lot about.”

It isn’t surprising, therefore, that many of the leading outside groups have jumped into that race behind McDaniel. Establishment Republicans in the state, including former governor Haley Barbour, have hit McDaniel over the Katrina comment. McDaniel has tried to repair the damage. His campaign quickly issued a statement saying he would have supported the funding, but he has stirred more controversy by suggesting there was considerable waste and fraud in the use of those funds.

Cochran’s support is broad but may be soft. McDaniel, despite his missteps, still presents a potentially serious threat, particularly because he can count on the outside groups for help in fundraising, for independent expenditure ads and for some limited grass-roots organizing.

“Ten years ago a guy like this wouldn’t have any money,” said one Republican strategist who backs Cochran but spoke on the condition of anonymity in order to offer analysis of the race. “They give him a fighting chance.”

Leaders of these outside groups acknowledge that defeating incumbents is, by definition, difficult but worth it to keep the party on a conservative path.

“We’re risk-takers,” said Chris Chocola, a former Indiana House member who now is president of the Club for Growth. “Our candidates are never the front-runner. If they were, we wouldn’t endorse them. Our win-loss record isn’t what our members judge us by. . . . If they don’t win, better to have fought and lost than not fight at all.”

That makes the continuing struggle for power inside the Republican Party one of the most important story lines of the 2014 elections.