(CNN) -- A celebratory Christine O'Donnell thanked her supporters, the Tea Party and kingmaker Sarah Palin on the night of her stunning win in Delaware's Republican Senate primary.
At the same time, party leaders were shaking their heads, watching helplessly as control of the Senate was slipping out of reach.
Republicans were expected to pick up the Senate seat that Vice President Joe Biden held for 26 years with Rep. Mike Castle, a nine-term congressman and popular former governor who appealed to independents and some Democrats, on the ballot.
And in an anti-incumbent year, Republicans had hopes of reclaiming the Senate, where Democrats hold 59 seats, including two independents who caucus with them, and Republicans 41.
But now that it will be O'Donnell facing off against Democrat Chris Coons, Democrats are breathing a little easier.
Within hours of the race being called, two top nonpartisan political handicappers changed their rating of how the Delaware Senate election might go.
The Rothenberg Political Report moved the race from "Lean Republican" to "Lean Democrat." On Wednesday morning, the Cook Political Report changed its rating from "Likely Republican" to "Likely Democrat."
"Castle had broad appeal, including to independents and even Democratic voters, while O'Donnell's appeal is limited to Tea Party conservatives. Lacking an impressive resume and unlikely to garner significant national Republican support, O'Donnell clearly looks like an underdog against New Castle County Executive Chris Coons (D), who is suddenly transformed to the favorite in the general election," the Rothenberg Report said. "While Tea Party activists are jumping for joy at the primary results, it's Democrats who will have the last laugh in Delaware."
The Tea Party is a populist, conservative movement that grew out of frustration over perceived overspending by the federal government. Tea Party activists say they feel Washington doesn't hear the voice of the people.
Moments after O'Donnell's victory, the National Republican Senatorial Committee offered a one-armed embrace to their new candidate.
"We congratulate Christine O'Donnell for her nomination this evening after a hard-fought primary campaign in Delaware," Rob Jesmer, the committee's executive director, said in a statement.
No second sentence. No predictions for November.
"The NRSC statement appears as tepid as the Republican Governors Association's initial statement following Rick Scott's victory in Florida," said Paul Steinhauser, CNN's deputy political director. Outsider Scott defeated party favorite Bill McCollum in August in Florida's gubernatorial primary.
Top Democratic strategist Steve Elmendorf said the Republicans "basically gave away a Senate seat."
"This woman cannot win. Just look at the tone of what the NRSC and Karl Rove said," he said.
Speaking on Fox News on Tuesday night, Rove, who was a top aide for former President George W. Bush, said the political newcomer does not "evince the characteristics of rectitude and sincerity and character that the voters are looking for," adding "there's just a lot of nutty things she's been saying."
O'Donnell brushed off Rove's remarks, saying, "It's a shame. He is the same so-called political guru that predicted I wasn't going to win."
"And we won, and we won big. So I think he is eating some humble pie and trying to restore his reputation," she told ABC in response.
The newly minted Republican Senatorial candidate said that while she'd love the support of establishment Republicans, she can forge ahead without it.
"They don't have a winning track record," O'Donnell said Tuesday night. "If they're too lazy to put in the effort that we need to win, then, so be it. We're going to win without them."
The Tea Party Express, which ran ads, sent mailers and organized rallies in support of O'Donnell, vowed an aggressive independent expenditure campaign for its candidate.
Following Tuesday's noticeably chilly reception, some Republicans showed signs of warming to her Wednesday.
Senate Republican leader Mitch McConnell of Kentucky said he would support and donate money to O'Donnell's campaign.
McConnell didn't respond when asked whether he thinks O'Donnell's victory would lead to a Democrat winning the seat and jeopardizing a possible GOP takeover of the Senate. However, asked if he thinks she will win the race, he responded, "I'm going to be supporting the nominee, and we'll hope for the best. We'd like to win the seat."
Sen. John Cornyn, chairman of the National Republican Senatorial Committee, released a statement clarifying the organization's involvement in the general election.
"Let there be no mistake: The National Republican Senatorial Committee -- and I personally as the committee's chairman -- strongly stand by all of our Republican nominees, including Christine O'Donnell in Delaware," he said.
Cornyn also said the the committee would send her a check for $42,000, the maximum allowable donation provided to nominees.
The winner of November's general election will fill out the remaining four years of Biden's final term. Biden stepped down from the Senate after his election in November 2008 as vice president. Former Biden aide Ted Kaufman was named as an interim replacement, but Kaufman is not seeking a full term.
CNN's Kristi Keck, Ed Henry, Dana Bash, Ted Barrett, Paul Steinhauser and Jessica Yellin contributed to this report.