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.