Illinois Senator Roland Burris has said he will not stand for re-election when his term finishes next year. Mr Burris has been dogged by ethics complaints since being appointed to his post by disgraced ex-Illinois Governor Rod Blagojevich.
He would have faced a tough battle to be the Democrats’ nominee in the race.
The senator, who denies any wrongdoing, says he would have had to spend too much time raising money, and not enough time on his senatorial duties.
“I was called to choose between spending my time raising funds, or spending my time raising issues for my state. I believe that the business of the people of the state of Illinois should always come first,” he said.
‘Dilemma’
Mr Burris’s senate seat was previously held by US President Barack Obama, but became vacant when Mr Obama entered the White House.
Under state law, it was Mr Blagojevich’s duty to pick a replacement for Mr Obama, but before he was able to make his choice, he was arrested and charged with attempting to “sell” the senate seat in return for campaign contributions and personal advancement.
He was later impeached and removed from office, but not before he had chosen Mr Burris to fill the senate vacancy, raising concerns that the new senator may have offered Mr Blagojevich something in return for the appointment.
At the time of his appointment, Mr Burris denied that he had spoken to any members of the governor’s team about the senate seat, but later acknowledged that he had discussed it with Blagojevich aides.
The transcript of a conversation released by investigators in May indicated that Mr Burris had spoken about the seat to Mr Blagojevich’s brother Robert - who was in charge of fundraising for the former governor.
“I mean, so Rob, I’m in a dilemma right now wanting to help the governor,” Mr Burris told Robert Blagojevich, according to the transcript.
“I will personally do something,” Mr Burris allegedly said.
Mr Burris has repeatedly denied wrongdoing and in June, prosecutors announced that they would not be charging him with any crime.
With Mr Burris out of the running, the race to become the Democrats’ nominee in the 2010 senate race will be hard-fought.
One leading contender - Illinois Attorney General Lisa Madigan - announced this week that she would not be entering the race, but state treasurer Alexi Giannoulias reportedly plans to seek the nomination, as does Christopher Kennedy, a Chicago businessman and son of the late Robert F Kennedy, and Chicago Urban League president Cheryle Jackson.
For the Republicans, Illinois Congressman Mark Kirk has expressed an interest in running, according to media reports.