She surged with an infusion of cash from the national Tea Party Express, and her victory quickly came to be seen as a test of the power of the populist, limited-government movement.
In the debate, O'Donnell was feisty and on offense, quickly seizing on Coons' self-description in his now-famous 1985 college essay "The Makings of a Bearded Marxist."
"You learned your beliefs from an articulate, intelligent Marxist professor . . . that should send chills up the spine of every Delaware voter," O'Donnell said.
Coons said that the title of the essay was a joke, based on his Republican roommates teasing him for registering as a Democrat. "I am not now, nor have I ever been, anything but a clean-shaven capitalist," the balding Coons said, drawing laughter from the audience in the hall.
O'Donnell is still missing in action on the campaign trail, her events (if any) not publicized; she refuses to talk to the state's major daily newspaper at all, has released no policy proposals, and she is getting crushed in the polls, trailing by up to 19 percentage points. Experts in Delaware politics say it would be difficult for her to win in a largely moderate state.
But the international media fascination with all things Christine continues, and university officials issued more than 200 press credentials. The campaign has revolved around controversial statements she made in the 1990s as a conservative cable provocateur, on Bill Maher's Politically Incorrect and other shows – most famously, when she admitted she had "dabbled into witchcraft" as an adolescent.
Her first television ad of the general election campaign began with O'Donnell saying into the camera, "I am not a witch." She said she was a common person who got fed up with Washington. "I am you," she said.
O'Donnell tried to steer the debate away from her old remarks. "This election cycle should not be about comments I made on a comedy show a decade and a half ago," she said. But O'Donnell's past as frequent candidate for Senate and her financial problems, including foreclosure and debt, came up anyway.
At one point, O'Donnell referred to multiple skits on Saturday Night Live, spoofing her as a witch. "You're just jealous you weren't on Saturday Night Live," she said to Coons. "I'm dying to know who will play me, Christine," he said.
She said that a tax lien was a result of an IRS computer error. "Leadership doesn't count on whether you fall, it counts on whether you get up," O'Donnell said.
Coons declined to attack O'Donnell on her finances, calling them a "distraction."
In the middle of the debate, moderator Wolf Blitzer asked O'Donnell whether she still believed that evolution was a "myth," as she said in 1998.
"What I believe is irrelevant," O'Donnell said. She said that local communities should be able to decide whether to teach creationism on an equal footing with evolution.
Nancy Karibjanian, of Delaware First Media, was co-moderator with CNN's Blitzer.
Pressed to name specific Supreme Court decisions with which she disagreed, O'Donnell stumbled. She said she was against judges "legislating from the bench," but could not name a case. "I know there are a lot," O'Donnell said, pausing, bringing to mind Sarah Palin's inability to say what newspapers she read in a CBS interview.
"I'm very sorry, right off the top of my head I can't remember one, but I'll put them on my website, I promise," she said.
At times, Coons seemed puzzled at how to respond to his opponent. "It took a couple of minutes to figure out what she was talking about," he said at one point. "There's so much there I don't even know where to start," Coons said, after O'Donnell argued that it was wrong to force candidates to publicly disclose their campaign donations because, she said, supporters who gave to her had been harassed.
The latest poll, a CNN/Time/Opinion Research survey released Wednesday, found Coons leading O'Donnell 57 percent to 38 percent among likely voters. Coons had the backing of 17 percent of Republicans, the poll showed. The survey's overall margin of error is plus or minus 2.5 percentage points.
Castle said Wednesday that he would not endorse in the Senate race, and would not indicate how he might vote Nov. 2.
"There were some personal issues and other aspects of my primary campaign that were very disquieting," Castle said on National Public Radio. "And for that reason I think [it] best just to leave it alone."
During the campaign, O'Donnell said Castle should "put on his man pants" and debate her, and her campaign insinuated that the married former governor was having a homosexual affair.
Contact staff writer Thomas Fitzgerald at 215-854-2718 or email@example.com.