IT'S A REPUBLICAN SEAT:

Democratic Sen. Ben Nelson of Nebraska will announce today that he is retiring after two terms, a serious blow to Democratic efforts to hold on to their majority in the chamber next November. [...]

The 70-year-old Nelson was considered one of the most endangered Democratic incumbents this cycle. GOP-affiliated outside groups have already dumped hundreds of thousands of dollars into TV ads bashing Nelson, while the Democratic Senatorial Campaign Committee spent over $1 million on its own ad blitz to bolster his image.

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