There are primary races in seven states today, but all eyes are on Delaware, where Tea Party upstart Christine O’Donnell is challenging GOP stalwart Michael Castle. That's not only because O'Donnell is a flaky candidate with anti-masturbation plank in her platform and an endorsement from Sarah Palin, writes Nate Silver on FiveThirtyEight.com, but because an O'Donnell win could undermine the GOP's chances of taking control of the Senate back from Democrats.
O'Donnell is one of two tea partiers—the other is Ovide Lamontagne in New Hampshire—who Silver says could, by winning today, cut the odds of the GOP retaking the Senate from 30% to just 16%. Both are seen as much weaker candidates against Democrats come November.
(Read more Christine O'Donnell stories.)