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Dave Weaver, Associated Press
Sen. Ben Nelson, D- Neb. responds to a question during an Associated Press interview Wednesday Dec 28, 2011 in his Omaha, Neb office. Nelson says he decided to leave the Senate after 2012 because he wants more free time, not because he's retiring.

OMAHA, Neb. — Democratic Sen. Ben Nelson of Nebraska says he doesn't think his decision not to run for a third term will automatically hand the seat over to Republicans.

Nelson told The Associated Press on Wednesday there's still plenty of time for the 2012 campaign, so Democrats shouldn't hesitate to jump in.

He also says he's confident he could have won re-election.

But other Democrats acknowledge they face an uphill battle to keep Nelson's seat in the party. The GOP field already is crowded with Nebraska Attorney General Jon Bruning, state Treasurer Don Stenberg, state Sen. Deb Fischer, and investment adviser Pat Flynn.

Nelson says he's not retiring, but he doesn't know what's next. He has more than $3 million in campaign cash he could give to other candidates in the future.