President-elect Barack Obama said he hoped to fulfil “the simple hopes and common dreams of all Americans” as he announced his resignation from the US Senate today.
The Illinois senator’s resignation, which was expected, will reduce the Democratic Party’s majority to a bare minimum for the so-called “lame duck” session which begins next week.
America’s first black president-elect called his four-year Senate term “one of the highest honours and privileges” of his life.
Mr Obama, currently the only black senator, said the people of Illinois would stay with him as he leaves the Senate to begin “the hard task of fulfilling the simple hopes and common dreams of all Americans as our nation’s next president”.
The Democrats will retain control only if Independent senator Joe Lieberman, who publicly campaigned for Republican John McCain, sides with them.
Mr Obama’s resignation will take effect from Sunday, but his Senate office will remain open for up to 60 days so that staffers can archive documents for his future presidential library and contact constituents.
Under Illinois state law, Democratic Governor Rod Blagojevich will name Mr Obama’s replacement for the remaining two years of his term.
Mr Blagojevich has said he expects to make a decision by the end of the year, and has ruled out appointing himself.
Potential candidates to replace Mr Obama are Jesse Jackson Jr, Jan Schakowsky, Illinois Senate President Emil Jones and Illinois Attorney General Lisa Madigan.
On Tuesday, Mr Obama appeared with another potential replacement, Iraq war veteran Tammy Duckworth, to commemorate Armistice Day, known as Veterans Day in the US.
She is a former congressional candidate and head of the Illinois Department of Veterans’ Affairs.