The Tea Party could be threatening the GOP.

In a stunning upset, marketing consultant Christine O'Donnell won the Republican Senate nomination in Delaware on Tuesday, edging out Rep. Mike Castle.

Conventional wisdom held that Castle, a fairly liberal Republican, was a shoo-in for the Senate seat — the general election was expected to be an easy victory.

But despite the Republican party's best efforts to boost Castle's campaign, O'Donnell, who was endorsed by Sarah Palin, won 53.1 percent of the vote. And the win could spell trouble for the Republican party.

Republicans were poised to take over the Senate, given that they had Delaware wrapped up. But O'Donnell's win means it's a distinct possibility — in fact, it's highly likely — that Delaware will send a Democrat to Washington.

One conservative blogger, however, says this won't necessarily be a bad thing. Ben Domenech writes that he'd rather the Republicans remain a conservative minority than a liberal or moderate majority.

In New Hampshire, Tea Party candidate Ovide Lamontagne took an early lead in the Republican Senate race over former Attorney General Kelly Ayotte, but Ayotte edged out Lamontagne as more ballots were counted. Ayotte was declared the winner Wednesday morning, but Lamontagne may still decide to seek a recount because the vote was so close.

To read more about the "GOP nightmare," click here.

For live coverage of the NH race, click here.