WASHINGTON Senator Byron Dorgan, a North Dakota Democrat, announced on Tuesday he will not run for another six-year term, a move that could threaten his party's 60-vote majority in the Senate.
Dorgan said his decision was not related to the prospect of a tough election battle this year but because he felt it was time to pursue other interests after 30 years in Congress.
"So, over this holiday season, I have come to the conclusion, with the support of my family, that I will not be seeking another term in the U.S. Senate in 2010," he said.
He said in a statement on his website -- here -- that he wants to write books, teach and work on energy policy in the private sector.
Another Democratic senator, Chris Dodd of Connecticut, was expected to announce on Wednesday that he will not run for re-election in November, The Washington Post reported, citing sources briefed on the decision.
President Barack Obama, a Democrat, praised Dorgan in a statement: "From fighting for our energy future to standing with North Dakota's families through difficult economic times, Senator Dorgan has been a trusted leader for his state."
Dorgan's surprise announcement could change the political balance in the Senate, where the Democratic caucus's 60-vote majority is exactly enough to overcome any Republican filibuster, a legislative roadblock.
"(Dorgan's) seat is now really one of the Republicans' best opportunities to take a seat from the Democrats," Jennifer Duffy, senior editor of the Cook Political Report, said in a telephone interview. "Psychologically, it doesn't send a positive message to Dorgan's colleagues and the Democratic base."
Republican National Committee chairman Michael Steele linked Dorgan's decision to the Democratic Party's alignment with President Barack Obama's policies.
"Today's announcement ... highlights just how vulnerable both Senate and House Democrats have become since deciding to walk in lockstep with President Obama's government-run policies," Steele said in a statement.
Dorgan might have faced a difficult re-election contest had North Dakota's popular Republican Gov. John Hoeven decided to challenge him.
A Zogby poll released November 22, 2009, found 55 percent of registered voters would have chosen Hoeven, compared with 36 percent for Dorgan in a theoretical matchup.
Historically, the majority party in Congress tends to lose seats in the first congressional election after a presidential election.
(Reporting by Deborah Zabarenko, editing by Alan Elsner)