In the latest skirmish between Tea Partiers and the GOP mainstream, grassroots insurgent Christine O'Donnell has pulled ahead of Rep. Michael Castle in polls leading up to Tuesday's GOP Senate primary in Delaware. Castle, a former governor and one of his state's best-known politicians, was once considered the runaway favorite, but O'Donnell, a champion of abstinence education and other conservative causes enjoyed a major bounce after receiving an endorsement from Sarah Palin. The GOP establishment is pushing hard for Castle, dishing dirt on O'Donnell's financial problems and other issues. Will it be enough to derail the Tea Party upstart? (Watch an MSNBC discussion about Castle's chances)

Backed by party muscle, expect Castle to prevail: With Republican leaders "furiously going after" O'Donnell, says Steven Benen at Washington Monthly, and with Castle's campaign suddenly spending money it planned to save for the general election campaign, Castle will likely "eke out a win." But the "wild eyed panic" at GOP headquarters is still justified — after Tea Partier Joe Miller's upset of Sen. Lisa Murkowski in Alaska last month, anything is possible.
GOP Senate primary heats up in Delaware"

The GOP is shooting itself in the foot: Mainstream Republicans are only turning voters against them by trying to "destroy" Christine O'Donnell, says Dan Riehl at Riehl World View. The Republican base is screaming for the party to back fiscal conservatives, but the establishment got behind Castle, despite his liberal voting record, simply because it thought he'd be palatable to fence-sitters. If "the only valid argument for Castle" is that he'll help win a Republican majority, "no sale."
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If Republicans pick O'Donnell, Democrats win: "Delaware is a blue state," says Nate Silver at The New York Times, which means that the "electoral prospects of Castle and O'Donnell there are wildly divergent." The centrist Castle is nearly a 95 percent favorite against Democrat Chris Coons, while O'Donnell would stand just a 17 percent chance of winning in November. In this case, if the Tea Party wins, Republicans lose.
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