The Tea Party pulled off a stunning upset in the Delaware Republican Senate primary Tuesday night as marketing consultant Christine O'Donnell defeated establishment favorite and nine-term Rep. Mike Castle, bolstering the GOP's far-right faction but stripping the party of the advantage it held in the general election matchup.
A Tea Party underdog was also poised to win the GOP Senate race in New Hampshire, putting another November GOP victory in doubt.
Aided by a last-minute endorsement from Sarah Palin, O'Donnell easily defeated Castle in the race to claim the Senate seat vacated by Vice President Biden, 53 to 47.
But Palin's backing apparently was not enough to help former New Hampshire Attorney General Kelly Ayotte overcome a late surge from lawyer Ovide Lamontagne.
Lamontagne had the support of some Tea Party activists who considered him more conservative than Ayotte, the GOP establishment pick.
Lamontagne would face Democratic Rep. Paul Hodes in the general election race to fill the seat occupied by Republican Sen. Judd Gregg, who is retiring.
O'Donnell's victory appears to have ended the career of one of Delaware's most popular political figures and throws into serious doubt the GOP's chances of winning the seat back from the Democrats in November.
While Castle was leading Democratic candidate Chris Coons by 11 points in the most recent poll, O'Donnell was found to be trailing him by 11 points.
In New Hampshire, Ayotte was leading Hodes by 8 points in August while Lamontagne trailed Hodes by about 3 points in July polling.
O'Donnell's win puts the national Republican apparatus in an awkward position. For days, the party has been attempting to salvage Castle's campaign by attacking O'Donnell over unpaid bills and accusing her of fraud.
The party even started a Web site dedicated to bashing her. It lists her unpaid debt, which includes a $90,000 default judgment from a mortgage company and more than $11,000 owed to the Internal Revenue Service. The site was up and running Tuesday night, even after O'Donnell was declared the victor.
Before her win Tuesday, O'Donnell had been a frequent candidate in the state, but had never won.
The Republican establishment will now either have to change course and embrace the candidate they once vilified, or abandon altogether a race they considered critical in their bid to retake the majority in the Senate or seriously reduce the Democratic advantage.
Tuesday's contests essentially conclude what has been a bitterly divisive primary season for Republicans. The GOP establishment watched seven of their candidates fall to more conservative newcomers pushed to the forefront by the Tea Party movement or an endorsement from Palin.
The party split was particularly ugly in Delaware, where state GOP Chairman Tom Ross said he has received a death threat over his support of Castle.
Castle was unable to survive a last-minute surge from O'Donnell, who had hammered him over his moderate voting record, including his vote in favor of a cap-and-trade bill. O'Donnell labeled him a liberal and declared herself the true Republican candidate.
Republican discontent played a role in the New Hampshire race as well. Ayotte was anointed one of Palin's "Mama Grizzlies" but she was also the GOP establishment candidate.
Some on the Republican right, however, viewed Lamontagne as the true conservative candidate. With endorsements from the state paper and Sen. Jim DeMint, R-S.C., Lamontagne had recently closed to within just a few points of Ayotte's once-sizable lead.