Democrat John Edwards is exiting the race for the White House after failing to win any of the four party nomination contests held so far, officials say.
His team said the former North Carolina senator had decided not to continue.
He lost Iowa's caucuses, came third in New Hampshire, admitted getting his "butt kicked" in Nevada and came third in his native South Carolina.
In the Republican field, ex-New York Mayor Rudy Giuliani is expected to drop out later and endorse John McCain.
Mr Giuliani came a distant third in Florida's primary on Tuesday.
It is not yet clear if Mr Edwards will endorse either of the two current Democratic front-runners, Hillary Clinton or Barack Obama.
He is expected publicly to announce the end to his White House bid in New Orleans, where he formally launched the campaign in 2006.
His website said he was to make a speech on poverty at a community project in the flood-ravaged Louisiana city on Wednesday at 1300 local time (1900 GMT).
The 54 year-old's withdrawal leaves the Democratic contest a two-horse race, say correspondents, pitting the New York senator and former First Lady, Hillary Clinton, against Illinois Senator Barack Obama.
The BBC's Vincent Dowd in Washington says if Mr Edwards urges supporters in one direction or another that could be an important influence in the race for the nomination.
http://news.bbc.co.uk/1/hi/world/americas/7217838.stm