There’s no doubt that the Tea Party could get the Republicans in trouble in certain races. In Nevada and Kentucky, for example, Sharron Angle and Rand Paul knocked off candidates preferred by the party establishment in order to win their primaries. Although the FiveThirtyEight model has both Ms. Angle and Mr. Paul as slight favorites the general election, the races are closer than they otherwise might be.
With Senator Lisa Murkowski’s concession late Tuesday night in Alaska, where she was defeated by the insurgent candidate Joe Miller, the Tea Party will have played a role in defeating two Republican incumbents (Robert F. Bennett of Utah is the other). In these two cases, the Tea Party is on much firmer tactical ground.
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Under certain circumstances, these dalliances with centrism might be something Republicans might tolerate. It is unlikely that a senator significantly more conservative than Ms. Collins or Ms. Snowe could be elected out of Maine; instead, the seat would probably default to a Democrat. But Ms. Murkowski and Mr. Bennett hail from Alaska and Utah, two of the most conservative states in the country (although Alaska is somewhat idiosyncratically so), and Republicans could afford to be picky.
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Democrats, meanwhile, mounted serious primary challenges to three of their incumbents: Arlen Specter of Pennsylvania, Blanche Lincoln of Arkansas, and Michael Bennet of Utah (the challenge succeed only in Mr. Specter’s case). None of these quite fit the paradigm.
http://fivethirtyeight.blogs.nytimes.com/2010/09/01/in-targeting-murkowski-tea-party-chooses-wisely/#more-515