Fringe Tea Partier Christine O’Donnell’s victory over the party-anointed Mike Castle in Delaware has hurt Republicans' chances of taking over the Senate—from 26 percent last week to 15 percent on Thursday, according to FiveThirtyEight’s Nate Silver. Castle had a 94 percent chance of beating the Democratic nominee, Chris Coons, but O’Donnell has a mere 6 percent chance. That means Republicans have to either sweep the Democratic-held seats currently considered competitive or put more seats in play. Seven Democratic seats are polling favorably for Republicans, and three more seats are close. The races to watch the next few weeks will be Washington state’s Patty Murray versus her Republican challenger, Dino Rossi, and Wisconsin’s Russ Feingold against Republican Ron Johnson. The race in California is the closest right now, with Barbara Boxer and Carly Fiorina polling within the margin of error. If Republicans don’t like those odds, they may try to put West Virginia and Connecticut in play.