But for the Republican Party — whose leaders had cast O'Donnell as unelectable and unstable — the vote in Delaware symbolized an identity crisis within the GOP that could complicate its push for big gains in the fall elections that will decide control of Congress.

Although O'Donnell won with a small percentage of votes in one of the nation's smallest states, her victory reverberated across the nation and widened a chasm separating conservative insurgents and their Tea Party allies on one side, and mainstream Republicans and centrists on the other.

"It's official: There is now a civil war within the Republican Party," said Mark McKinnon, a former adviser to the presidential campaigns of George W. Bush and John McCain. "The good news for Republicans is the Tea Party is capturing the anti-establishment energy in America. The bad news is that includes the Republican establishment."

For months, lingering unemployment and slipping support for President Obama's health care law and economic stimulus package have boosted GOP hopes for a tidal wave on Nov. 2 that would put the party back in power — a repeat of the 1994 "Republican Revolution" during the middle of President Clinton's first term.

Tea Party, O'Donnell win is not a shocker

In a year when Republicans need a net gain of 10 seats to reclaim control in the Senate, the Tea Party's successes in states such as Nevada and Colorado could complicate that effort by giving Democrats targets they see as easy to attack. Sen. Robert Menendez, a New Jersey Democrat in charge of his party's effort to hold its Senate majority, said chances have improved because Republicans have "run extremists instead of mainstream candidates."

O'Donnell's upset win in Delaware was a fitting climax to a tumultuous primary season in which voters in both parties turned out seven members of Congress — four Republicans and three Democrats — and, in the name of change, selected political newcomers over more experienced candidates in states such as Nevada, Kentucky and New York.

"There are a lot of people who are rallying behind me who are frustrated that the Republican Party has lost its way," O'Donnell told the Associated Press.

Rep. Bob Inglis, a South Carolina Republican who was one of the Tea Party's first casualties this year, said the small-government movement is elevating "flame throwers" over legislators. "I'm concerned that we're losing a focus on solutions," he said.

O'Donnell, 41, had sought the Senate seat twice before, but her right-leaning positions and thin political résumé had always relegated her to also-ran status in blue-leaning Delaware. This time around, the mood matched the candidate.

The Senate seat was held for 36 years by Democrat Joe Biden, who defeated O'Donnell 65%-35% in 2008. He gave up the Senate seat to become Obama's vice president. Biden friend and longtime aide Ted Kaufman, who was appointed to fill the seat until this year's election, chose not to run.

O'Donnell and Castle, a popular former governor and nine-term member of Congress, have similar views on economic issues and the Democratic agenda — both supported repealing Obama's health care law. But they differ sharply on social issues, and O'Donnell managed to cast the centrist Castle as a "liberal."

Castle supports a woman's right to an abortion but opposes late-term procedures. O'Donnell opposes abortion rights.

"Republican voters have become more conservative on social issues and increasingly frustrated with national policy," said University of Delaware political scientist Joe Pika. That, he said, made a target of "anyone who would compromise with its architects, even infrequently."

O'Donnell, a New Jersey native and self-described marketing consultant, also got a boost when a little-known lawyer named Joe Miller upset incumbent Sen. Lisa Murkowski in Alaska's Aug. 24 GOP primary. Miller had the help of former GOP vice presidential nominee Sarah Palin and the California-based Tea Party Express. The election underscored the potential for candidates running anti-establishment campaigns.

"Alaska has energized my base," O'Donnell said after Miller's victory. She eventually got the support of Palin and the Tea Party Express.

But unlike in Alaska, Delaware's primary turned nasty.

State Republicans attacked O'Donnell for $11,744 in unpaid income taxes that resulted in an IRS lien against her in March, which she blamed on a computer glitch. She had to explain to The News Journal in Wilmington, Del., that she received a degree from Fairleigh Dickinson University this year — 17 years after attending classes — because she had owed $4,000 in tuition.

The acrimony flowed both ways. Castle spokeswoman Kate Dickens said Wednesday the congressman would not endorse O'Donnell in the fall because of the "lies" she said the Republican had spread about his positions and his family. At one point, O'Donnell supporters erroneously suggested that Castle might switch parties if elected.

But it is her conservative positions — not her personal life — that Democrats began attacking immediately after she won the nomination Tuesday.

O'Donnell, who is single and has no children, founded a group in Washington, D.C., called Savior's Alliance for Lifting the Truth that focused on promoting Christian values and occasionally took controversial positions on homosexuals and sexual issues.

"We need to address sexuality with young people," she told MTV in 1996. "The Bible says that lust in your heart is committing adultery. And you can't masturbate without lust."

Hours after O'Donnell won, Delaware's Democratic Senate nominee, county executive Chris Coons, began casting her positions as "ultraconservative." On his website, the campaign says O'Donnell "has a record of supporting discrimination against gays and lesbians, and pressing for public schools to teach creationism."

In an interview Wednesday, Coons said the squabbling in the GOP primary probably turned off voters. He promised to stay above the fray. "There are tens of thousands of people in Delaware who are anxious, who are angry," he said. "They want change."

But whether the message sent in the primary will resonate in the general election remains unclear. Just more than 55,000 voted in the primary — about 30% of Delaware's registered Republicans. In the general election, Democratic voters outnumber Republicans, 292,738 to 182,796.

Will Dems have 'last laugh'?

While O'Donnell celebrated her improbable victory, so did Democrats.

Party leaders and non-partisan analysts agreed that Coons was helped by GOP voters' elimination of Castle, whose political crossover appeal helped him win 12 statewide elections.

Menendez, the chairman of the Democratic Senatorial Campaign Committee, said his efforts to keep the Senate majority are improved because of victories by O'Donnell and other Tea Party candidates in key states.

"We are demonstrably more competitive in a handful of states," he said. Among them: Kentucky, Connecticut, Colorado and Nevada.

In Delaware, Castle was heavily favored to pick up Biden's Senate seat. Within minutes of O'Donnell's victory, however, political handicappers changed their assessment of the Delaware Senate race from a likely Republican pickup to a likely Democratic win.

"While Tea Party activists are jumping for joy at the primary results, it's Democrats who will have the last laugh in Delaware," Stuart Rothenberg wrote in his non-partisan political newsletter. And if Republicans can't pick up the Delaware seat, it will be much more difficult for them to find the 10 seats they need to take control of the Senate, Rothenberg told USA TODAY.

"It doesn't end the possibility, but it makes it a lot harder," he said.

The Republican in charge of his party's Senate campaign, Sen. John Cornyn of Texas, was not trumpeting the possibilities of a GOP takeover. "It's a theoretical possibility but that's not what I'm predicting," he said. "I think it's going to take two election cycles."

Others, however, argued that the volatility of the election results so far leaves open the possibility of more upsets in November.

Public opinion polls gathered by Realclearpolitics.com indicate victories are within reach for some rookie GOP Senate candidates, such as Tea Party favorites Rand Paul in Kentucky and Sharron Angle in Nevada, as well as Linda McMahon in Connecticut.

O'Donnell, too, may outperform expectations, said longtime GOP strategist Ed Rollins.

Although Democrats "may be licking their chops" at the prospect of a campaign against her, he said, "some of the other candidates they said weren't going to work out have worked out pretty well."

A 'unified' party?

The fractures in the GOP started to show last spring, when veteran Republican senator Robert Bennett of Utah was kept off the GOP primary ballot by Tea Party supporters and other conservatives who blasted him for voting for the government bailout for Wall Street.

Then Paul, a Tea Party favorite, beat establishment-backed Trey Grayson, the choice of Senate Republican leader Mitch McConnell, in the Kentucky primary.

Other Tea Party victories have followed, but the O'Donnell-Castle fight widened the schism between grass-roots conservatives in the Tea Party and the GOP establishment.

Before the election, state GOP chairman Tom Ross said O'Donnell "could not be elected dog catcher." GOP strategist Karl Rove, architect of George W. Bush's White House victories, described O'Donnell on Fox News as "nutty" and a person "with serious character problems."

By Wednesday morning, party leaders were rushing to repair the rift. Cornyn said he had a "nice conversation" by phone with O'Donnell, who just hours before had publicly challenged the Senate campaign committee to support her. Cornyn said the National Republican Senatorial Committee would cut her a check for $42,000. But the committee could pour millions more into the race by paying for a separate advertising campaign. Cornyn would not commit to additional resources, saying he'd wait to see how the general election campaign unfolds.

Cornyn acknowledged he was "surprised" by O'Donnell's win and didn't sugarcoat the impact of the past few months on his efforts. "Primaries are hard," he said. "I am glad they are over." He said the GOP will coalesce around its nominees.

Not all conservatives were satisfied.

"The Republican leadership still doesn't get it," said Brent Bozell, who heads a watchdog group that monitors the news media for liberal bias. "In race after race, they backed moderate to liberal candidates over the conservatives." After the Tea Party victories, the party leadership is "like a deer in the headlights."

The Tea Party's successes so far are "shaking the establishment," said Sen. Jim DeMint, a South Carolina Republican, adding that colleagues "kind of laughed at me" when he began providing financial and campaign support to O'Donnell and Paul while the party establishment was backing their rivals. He sounded a conciliatory note Wednesday.

"The party today is unified," DeMint said.

The next Congress however, seems almost certain not to be. On Tuesday, as Tea Party activists were celebrating conservative victories, liberal activists in the Democratic Party were hailing the defeat of Katrina Swett in a New Hampshire congressional primary by a more left-wing candidate.

"Tolerance for any deviation from party orthodoxy is at an all-time low," said Sen. Evan Bayh, a moderate Democrat from Indiana who is retiring this year, in part because of the polarized atmosphere on Capitol Hill. "It used to be that principled compromise was thought to be a good thing. Now it's viewed as an act of treachery."

An election year that has winnowed Congress' ranks of centrists is "going to make this place even more gridlocked and ideologically divided than it is now," Bayh concluded. "And that's hard to imagine."

Mixed outlook for Tea Party candidates in November

The Tea Party movement has scored some big wins in Republican primaries for the Senate, but its prospects for success in the fall are mixed.

Back story from the primary Big upset: Miller edged incumbent Sen. Lisa Murkowski, who may run as an independent. Buck defeated Republican establishment-backed Jane Norton. The shocker: O'Donnell, a long shot who lost twice before, defeated nine-term Rep. Mike Castle. Paul trounced Trey Grayson in a rebuke to Senate Minority Leader Mitch McConnell. Angle trumped two better-known Republican candidates. Senate Democratic leader Reid seen as prime GOP target. Incumbent Sen. Robert Bennett finished third to two Tea Party candidates at the state GOP convention.