(CNN) -- Nine-term Republican Congressman Mike Castle finds himself in a tight primary race with TV commentator and Tea Party favorite Christine O'Donnell in Delaware's Republican U.S. Senate primary on Tuesday.
In the closing days of the primary campaign, O'Donnell has gotten a boost with an endorsement by former Alaska Gov. Sarah Palin and more than $150,000 in late spending from the Tea Party Express. All this has the Republican establishment worried that O'Donnell could take down the Republican they believe is best positioned to win in November.
O'Donnell has positioned herself as a conservative gate-crasher.
"We're breaking up the backroom deals," she told CNN. "We're restoring the political process back to the hands of the people." She refers to Castle as the "anointed one."
In an interview that was certainly free of the usual talking points she told CNN:
-- The Republican Party is behind "false accusations and attack ads" against her and accused party operatives of "fighting for not only my opponent's political career but their own political career."
-- She believes its "a shame" that FreedomWorks, the Dick Armey group that backs Tea Party candidates, declined to endorse her but disagrees with the organization's view that she can't win the general election saying, "No one even thought we could get this far."
-- As for Democrats who think she'll be the easier candidate to beat in November she says, "To those Democrats, I say, 'Send a donation my way. Let me run more ads. I can make sure that I win [the primary] if you think that it'll be that easy.' "
-- Sarah Palin's endorsement "is helping a lot" because "it gave my supporters an extra boost of encouragement." And it helped her too: "Governor Palin can relate to the politics of personal destruction and she's survived them and they didn't get her down."
-- And she says she'd love support from one well-known Democrat: "I Would love Hillary Clinton's endorsement. When I saw her presidential ads I said, 'You go, girl!' I'm a Republican, so I probably won't vote for her but I do admire her."
Democrats are positively gleeful at the prospect of an O'Donnell victory on Tuesday. Many had written off Vice President Joe Biden's old Senate seat as a loss. But if O'Donnell wins, Democrats believe they'll hold the seat in November, which could save their majority in the Senate.
Castle's team insists its internal polling still shows him with a lead and the well-known Republican told CNN affiliate WPVI his opinion of the O'Donnell surge.
"I really don't buy it," Castle said. "We've been doing our own polling, obviously, and we're comfortable."
The big unknown is election-day turnout. There are fewer than 183,000 registered Republicans in the state. It's a closed primary -- meaning neither Democrats (approximately 293,000 registered voters) nor independents (146,00 registered as "other") can vote. And in an off-year primary, very few voters tend to turn out.
So this race -- and perhaps the balance of power in the Senate -- could be decided by fewer people than usually turn out for a Sarah Palin rally.