Nati Harnik, Associated Press
FILE - In this Oct. 9, 2008 file photo, former U.S. Sen. Bob Kerrey speaks during a healthcare debate in Lincoln, Neb. The former one-term Nebraska governor and two-term U.S. senator said Tuesday, Feb. 7, 2012 that he won't seek the Democratic nomination for Nebraska Senate seat he formerly held to replace U.S. Sen. Ben Nelson, D-Neb.

OMAHA, Neb. — Former Sen. Bob Kerrey said Tuesday he will not run for the Nebraska Senate seat he gave up more than a decade ago, shutting down hopes for a bid both parties called Democrats' best chance to hold the seat.

The 1992 presidential candidate and former Nebraska governor considered seeking the Democratic nomination to succeed Sen. Ben Nelson, but also had called his chances of winning in November a longshot.

Nelson's decision not to run for a third term this year came as a boon to Republicans, who must net four seats to retake the Senate and have made capturing the lone remaining Democratic seat in Nebraska's congressional delegation a priority.

"I have given the decision of becoming a candidate for the U.S. Senate very serious thought and prayer," Kerrey said in an email announcing his decision. "To those who urged me to do so, I am sorry, very sorry to have disappointed you. I hope you understand that I have chosen what I believe is best for my family and me."

Kerrey, who moved to New York City after giving up his seat in 2001, spent nearly a week in Nebraska last month to seek advice about whether to run in a state that has drifted ideologically away from him since he left.

After his announcement, he told The Associated Press in a telephone interview from his New York City office that he was not pressured by the Democratic Party.

"I made it very clear at the beginning that I couldn't be talked in and couldn't be talked out, other than my own assessment of what was right and good for my family," Kerrey said.

Of course, Kerrey has a history of mulling campaigns he never enters. He did so in 2000, when he considered another run for president, as well as in 2005, when he toyed with running for New York City mayor. His last came in 2008, when he again stepped away from a run for Nebraska's last open U.S. Senate seat, now held by Republican Mike Johanns.

Republicans this time around would have been sure to hammer on Kerrey's decision to leave the Senate and become president of the New School, a self-described progressive university in Greenwich Village. Kerrey did stay involved with government, working as a member of the 9/11 Commission, but the GOP would have highlighted his time away from increasingly conservative Nebraska.

"I would say if you bet ... you'd have to bet against me," Kerrey said last month. "I've been away 11 years. I'm a Democrat. Obama's going to top the ticket, and he's probably going to be unpopular. So I'd say the odds are probably not good."

Republicans had acknowledged Kerrey as a possibly formidable presence in the race. Nebraska's airwaves already had been peppered with political ads by conservative groups portraying Kerrey as "an East Coast liberal" who supports universal health care and taxpayer-funded abortion.

Kerrey had brushed aside the ads, noting he was "attacked virtually every day for being a right-winger (who) supported George Bush's war in Iraq" during his time at The New School.

The National Republican Senatorial Committee said in a Tuesday statement that "Kerrey's decision to stay in New York is a blow to the Democrats' hopes of holding their Senate majority and reiterates why we believe Nebraskans will elect a fiscally-responsible, conservative Republican Senator next fall."

The GOP ticket for this year's Senate race already is crowded. It includes Nebraska Attorney General Jon Bruning, state Treasurer Don Stenberg, state Sen. Deb Fischer, and investment adviser Pat Flynn. But party insiders have said Heineman was under pressure to run from high-level Republicans who feared Kerrey would run and win.

Heineman had been widely expected to seek the seat this year, but instead announced two days after his re-election as governor in 2010 that he wouldn't run. He has stood by that decision since.