When Kerrey retired in 2000, the Dems had a recent governor ready to run (Ben Nelson, who was term-limited in 1998); they have no such candidate this time around. The only Dem governors of NE during the past 40 years have been soon-to-be-ex-Senator Nelson, ex-Senator Kerrey, and late ex-Senator Exon.
And here's the latest "update":
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On December 27, 2011, Political Wire reported that Nebraska Senator Ben Nelson would not seek re-election, and asserted that Kerrey was in talks with senior Democrats about the possibility of replacing him.[22] The Washington Post reported that Kerrey would neither confirm nor deny the rumor.[23] ==============================================
I wouldn't put it past the NE 'RATs to "persuade" Kerrey into "un-retiring" for the "good of the party", like they did with Lautencorpse in NJ.