According to early projections of the result of yesterday's US Super-Tuesday poll, John Kerry picked up at least 88 delegates for a total of 201. Edwards picked up 59 for a total of 100, putting him in third place behind Dean, who picked up 3 for 117. Clark picked up 24 for a total of 55.
Lieberman had been hoping for a win in Delaware, but dropped out after meeting with staff members and conferring with his family.
"I have decided tonight to end my quest for the presidency of the United States of America," Lieberman said at a rally near his campaign headquarters in Arlington, Virginia.
Tuesday's votes offered the first nationwide test for the candidates, who spent almost all of January battling in Iowa and New Hampshire, largely white and rural states that hosted the first two nominating tests.
South Carolina was the first contest in the South and the first in a state with a large black population, while Arizona and New Mexico hold the first contests in states with large Hispanic populations.
Kerry, whose rise has been fuelled by a belief among Democratic voters that he offers the best chance to beat Bush in November, pointed to public opinion polls that showed him leading Bush in a one-on-one matchup.
Network exit polls showed Democrats across the country rallied to Kerry because they thought he could beat Bush. They cited the economy, jobs and health care as their biggest concerns, with Iraq and fears of terror receding.
The race moves next to Michigan and Washington on Saturday, Maine on Sunday, and Virginia and Tennessee next Tuesday.
Dean, struggling to halt his downward slide after dismal finishes in Iowa and New Hampshire, continued his string of poor showings on Tuesday. A close third place in New Mexico was the strongest finish for Dean.
Dean, who spent election night in Washington, looked ahead to Michigan, Washington and to a February 17 showdown in Wisconsin. He promised to push ahead into March.
"We are going to have a tough night tonight," Dean told supporters in Tacoma, Washington, but promised the state's contest on Saturday would be "a turning point" for his fading campaign.
While Tuesday offered a rich harvest of delegates to the nominating convention, only about 10 percent of the total delegates were allocated by the end of the night.
Dean, Edwards and Clark hope to extend the race to March 2, when huge, delegate-rich states like New York and California vote.