Berkshire Hathaway CEO and Omaha native Buffett emerged as a political player last year when President Obama named a proposed rule to raise tax rates on the wealthy after him. He has campaigned for Obama, but typically is known for shying away from public events.

Kerrey, a former Nebraska governor, in a tough race with opposition from well funded Republican groups and grassroots activists who helped Sarah Palin-backed Republican candidate Deb FischerDeb FischerLawmakers share photos of their dogs in honor of National Puppy Day Senators demand Pentagon action after nude photo scandal GOP rep scolds Gillibrand for tearing into Marine general over nude-photo scandal MORE win the primary last month. 

The Hill rates the race as "likely Republican."