Now the GOP establishment wonders if the grass-roots movement will power Republicans to new victories in 2012, or dash them on the rocks of unbending ideology.
One thing is obvious: The tea party already is reshaping the Republican Party. Once-moderate lawmakers are shifting sharply right, fearing primary challenges more than Democratic opponents. And most GOP presidential contenders have positioned themselves to the right of party leaders, and even some House tea partyers, on the debt-ceiling issue.
The movement's influence on the GOP remains double-edged. Tea partyers' adamant opposition to tax hikes helped Republican Party regulars force President Barack Obama to surrender his push for new taxes on the rich. But House tea partyers also embarrassed Speaker John Boehner by forcing him to hastily revise his debt-ceiling bill.
To secure their votes, Boehner added a balanced-budget provision that had no hope of becoming law, and which drew ridicule from some quarters. A weakened requirement that the House and Senate only vote on -- not necessarily pass -- a balanced budget amendment before the end of the year survived in the final product.
With the tea party about to play its first role in a presidential election, mainstream Republicans hope to harness its energy in campaigns nationwide, as they did in 2010. The trick is to do it while avoiding the damage of that year, when tea partyers cost the GOP likely Senate pickups by nominating out-of-the-mainstream conservatives in Delaware, Nevada and Colorado.
The lesson, party insiders say, is not for the tea party to dampen its fire. Rather, they say, Republican candidates must understand its power. Shame on those who get blindsided this time.
The tea party is "driving the conversation," said Republican consultant Danny Diaz. "The president, Congress, Democrats, Republicans are all talking about austerity, restraint, the spending crisis. That's not going to change."
Asked if another tea party insurgent might cost Republicans a likely Senate win, as Christine O'Donnell did last year in Delaware, Diaz put the onus on the party's candidates. "If you are seeking office in this environment," he said, "it would behoove you to discuss the out-of-control spending that's taking place in Washington."
Another Republican consultant, Brian Nick, agreed. "A candidate has got to figure out a way to get through a primary," he said, and it's unfair to make scapegoats of tea partyers. Veteran elected Republicans with mainstream conservative histories have gotten the message. Some are virtually reinventing themselves as tea partyers.
In Utah, already-conservative Sen. Orrin Hatch has veered so hard to the right that it's a constant topic of conversation, and sometimes amusement, in state political circles. Still, many wonder if he can survive if freshman Rep. Jason Chaffetz, a tea party favorite, decides to challenge him.
In New Mexico, former five-term Rep. Heather Wilson built a reputation as a GOP centrist, willing to buck her party's leaders and support raising the minimum wage and expanding children's health insurance. In 2008, she lost a Senate primary to a more conservative Republican.
Now, running for Senate again, Wilson has pledged to oppose raising the nation's debt ceiling unless Congress passes a balanced budget amendment to the Constitution. That requires a two-thirds majority in both chambers, which lawmakers in both parties say is politically impossible.
Virginia Republican George Allen, who is trying to regain the Senate seat he lost in 2006, has taken a similar stand, even though he voted four times to raise the debt ceiling while in office.
Many congressional Republicans support the balanced-budget amendment. In the end, however, a solid majority of them, including most members of the House tea party caucus, voted for the bipartisan debt-limit deal that dropped a demand that the amendment first win passage and be sent to the states for ratification.
The big unknown is the tea party movement's influence on the presidential race. Some political professionals think tea partyers already are pushing GOP candidates so far right that the eventual nominee might struggle to pick up independent voters in the general election against Obama. Former Massachusetts Gov. Mitt Romney appeared unenthusiastic when announcing his opposition to the debt-ceiling compromise that Congress enacted with solid GOP support in both chambers.
Jon Huntsman, the only presidential hopeful to support the measure, said Romney did not show leadership.
The tea party's influence on the GOP "will come with heavy baggage in independent-leaning states like Maine or even Indiana," said Nate Daschle, a Democratic activist whose father was Senate majority leader. That could apply to Senate races in those states, where incumbent Republicans face tea party challengers for the nomination, and to the presidential race, he said. Obama won Indiana narrowly, and Maine handily, in 2008.
Independent voters skip most primaries but play big roles in general elections. They want "progress over rigid ideology," Daschle said.
If tea party voters dominate GOP primaries, they can nominate unorthodox candidates such as Delaware's O'Donnell.
"The tea party didn't happen by accident and it wasn't contrived," Daschle said. "It's one of the purest and most organic movements in politics today, and while it may endanger its parent party, this is exactly the way the system was designed."
A recent Pew Research/Washington Post poll suggests that Republicans did themselves few favors in the debt-ceiling struggle. About four in 10 Americans said they had a less favorable view of congressional Republicans because of the negotiations, while three in 10 said their opinion of Democrats in Congress faded. People who now have a dimmer view of tea party-affiliated lawmakers, because of the debt issue, outnumber those with a more positive view.
A CBS News/New York Times poll this week shows that only 20 percent of Americans and 41 percent of Republicans have a favorable view of the tea party, down from 26 percent and 59 percent, respectively, in April. Just 18 percent of Americans now view themselves as tea party supporters, compared with 31 percent who did immediately after the November 2010 elections.
Texas Tech University political scientist Tim Nokken warns against overstating the tea party's influence. "I'm not sure the GOP is going to march lock-step with the tea party," he said in an email.
The movement may have its biggest impact on Republican House members eager to avoid a primary threat from the right, he said. These lawmakers may act "not so much out of agreement with the tea party agenda, but as a means to reduce the likelihood of a primary challenge," Nokken said.
Either way, the tea party is leaving a big mark on the GOP. And the limits of its influence are not yet clear.