Two veteran Democratic senators have announced that they will retire instead of running for re-election, in what may be a sign that Democrats could face a tough time at the polls in mid-term elections in November.  It is a shaky political start to 2010 for Democrats, who currently control both houses of Congress.

First it was Democratic Senator Byron Dorgan of North Dakota who shook up the political establishment Tuesday by announcing he would not seek re-election.  Analysts say his retirement boosts Republicans' chances of capturing the seat in November.

Next came Connecticut Democratic Senator Christopher Dodd, the chairman of the powerful Senate Banking Committee, who announced his decision not to run for re-election for a sixth term.

The loss of either seat would deprive the Democrats of their 60 vote majority in the Senate and give the opposition Republicans the power to block legislation they do not like.

Opinion polls indicate Senator Dodd's popularity has declined sharply, and he admitted he has had a rough year.

"I lost a beloved sister in July and, in August, [Senator] Ted Kennedy," said Christopher Dodd. "I battled cancer over the summer, and in the midst of all of this, found myself in the toughest political shape of my career."

The White House issued a statement praising Dodd for dedicating his life to public service.

Senator Dodd was at the center of efforts to reform the U.S. financial system and health-care reform legislation. 

He says he is not retiring to spend more time with his family, an excuse used by many departing politicians.

"I have been a Connecticut senator for 30 years," he said. "I am very proud of the job I have done and the results delivered.  But none of us is irreplaceable.  None of use are indispensable.  And those who think otherwise are dangerous."

Political analyst Larry Sabato of the University of Virginia said Dodd's decision to retire actually gives Democrats a much better chance of winning that Senate seat in November.

"When you look at the two seats, you realize that in fact the Democrats have now saved Connecticut," said Larry Sabato. "They were going to lose with Dodd and now they have a much stronger Democrat as the presumptive nominee, the Attorney General Richard Blumenthal."

But Sabato and other political analysts say the sudden string of retirements reflect a harsher political climate for Democrats across the country, after their electoral triumphs with President Obama and big wins in the House and the Senate in 2008.

"And you have to add these two retirements to the other shockers that have occurred within 24 hours," he said. "The Lieutenant Governor of Michigan who was the nominee presumptive governor in that heavily Democratic state withdrew his candidacy because he could not raise money.  Now the Democrats do not even have a strong candidate for governor and the Republicans, I think, are very, very likely to win the Michigan governorship."

Sabato said another setback for the Democrats is expected in Colorado.

"And then you look to Colorado where everyone there is stunned in both parties that Governor Bill Ritter, a first-term freshman Democrat is not running for a second term," said Sabato. "No one saw that coming, and that also opens up the possibility of a Republican takeover in a swing state that was very important to President Obama's victory in 2008."

Democrats hold a majority in the Senate with 60 votes, allowing them to pass sweeping health-care reform legislation without a single Republican vote.  But the current defensive political climate could hurt fundraising efforts for the November election, and could also force President Obama to scale back his ambitious domestic political agenda.