**US Senator Chris Dodd, a key ally of President Barack Obama, has announced that he will not seek re-election in November.**Mr Dodd’s move follows the decision by fellow Democratic Senator Byron Dorgan not to stand again.
The Democrats have 60 Senate votes, just enough to overcome Republican efforts to block legislation.
The balance of power could change after November’s elections, when a third of the 100 Senate seats will be contested.
Voters will also elect all 435 members of the House of Representatives.
Senator Dodd, who chairs the Senate banking committee, made the announcement that he would not be seeking re-election for a sixth term at his home in East Haddam, in the state of Connecticut.
“In the long sweep of American history there are moments for each elected public official to step aside and let someone else step up. This is my moment to step aside,” Mr Dodd told reporters.
Embattled
The 65-year-old Connecticut senator has been a key figure in efforts to deal with the financial crisis, and the healthcare debate.
However, Mr Dodd, a former presidential hopeful, has been increasingly embattled since 2008 amid criticisms over a loan he received from a subprime lender.
Opinion polls have suggested that he would not win re-election in November. Correspondents say his decision to retire would allow the Democratic Party to field a stronger candidate.
However, the decision by Senator Dorgan not to seek re-election in North Dakota is being seen as a big blow to the Democrats.
The Democrats, with the help of two independents, currently have a 60 to 40 seat majority in the Senate - the threshold number that allows them to override Republican attempts to hold up legislation.
The party in power in the White House tends to lose congressional seats in mid-term elections.