With the 2010 election year barely under way, two senators and one governor — all Democrats — ditched plans to run for re-election in the latest signs of trouble for President Barack Obama's party.

Taken together, the decisions by Sens. Chris Dodd of Connecticut and Byron Dorgan of North Dakota as well as Colorado Gov. Bill Ritter caused another bout of heartburn for Democrats as they struggle to defend themselves in a sour political environment for incumbents, particularly the party in charge.

As 2009 ended, Democrats watched a string of their House members announce retirements and one congressman defect to the GOP.

Now, with Dodd, Dorgan and Ritter out, Republicans have even more to crow about, if not better opportunities to pick up Democratic-held seats.

Democrats, who have a 60-40 Senate majority that includes two independents who vote with them, now will have to defend four open seats in the Senate. The others are Delaware and Illinois, where Sens. Ted Kaufman and Roland Burris were appointed to the seats vacated by Vice President Joe Biden and Obama. Kaufman and Burris are not running for election to the seats.

Among governors, Democrats are seeking to maintain their 26-24 majority in a year when those elected will oversee the redrawing of congressional and legislative districts for the next decade.

Republicans and Democrats alike say they now expect competitive races for the Senate seat in North Dakota, a GOP-tilting state, and the governor's seat in Colorado, a pivotal swing state that has trended toward Democrats in recent years but may be shifting back toward Republicans.

But in Democratic-leaning Connecticut, Dodd's retirement may actually heighten the likelihood that the seat he's held for five terms will remain in Democratic hands. The party can now recruit a more popular candidate to run, bolstering the prospects of thwarting a Republican victory.

Longtime Connecticut Attorney General Richard Blumenthal told The Associated Press on Wednesday morning that he will run for Dodd's seat. Blumenthal, a Democrat, is seen as one of the state's most popular politicians. He planned to publicly announce his candidacy later Wednesday.

Considered by many insiders to be the most endangered Senate Democrat, Dodd planned to announce his retirement Wednesday, according to Democratic officials who spoke on the condition of anonymity because they weren't authorized to publicly pre-empt the senator's remarks. Dodd told Democrats of his plans late Tuesday and scheduled an announcement on Wednesday.