Republicans are close to anointing John McCain as their presidential nominee following the surprise withdrawal from the race yesterday of his chief rival, former Massachusetts governor Mitt Romney.
Mr Romney's departure, which he announced at a conservative conference in Washington, leaves former Arkansas governor Mike Huckabee as the only challenger to Mr McCain.
Mr Huckabee upset expectations by winning five states on Super Tuesday and his campaign manager, Chip Saltsman, said the former Baptist minister had no plans to leave the race.
"We're still in the race and we're still competing for delegates, and today demonstrates how long and windy to the White House this is," he said.
Mr Romney, a former businessman who has lent his campaign at least $35 million from his personal fortune, said he was stepping aside to allow Republicans to unite in advance of November's election.
"If I fight on in my campaign, all the way to the convention, I would forestall the launch of a national campaign and make it more likely that Senator Clinton or Obama would win. And in this time of war, I simply cannot let my campaign be a part of aiding a surrender to terror," he said.
Mr Romney outspent all his rivals for the Republican nomination but he struggled to connect with voters and failed to unite conservatives around his candidacy.
He faced questions about his Mormon faith and about his shifting positions on social issues such as abortion and gay rights.
"This is not an easy decision for me. I hate to lose," Mr Romney said yesterday. "My family, my friends and our supporters . . . have given a great deal to get me where I have a shot at becoming president. If this were only about me, I would go on. But I entered this race because I love America."
Mr Romney said he was "suspending" his nomination, a technical distinction that allows him to continue raising money in an effort to recoup the loans he has made to his campaign.
The prospect of an early end to the Republican race gives Mr McCain an important advantage ahead of November's election, allowing him to consolidate support while Democrats Hillary Clinton and Barack Obama remain locked in battle for weeks to come.
Mr McCain has an uphill task in winning over conservatives within his party, many of whom are suspicious of him, but Republicans have traditionally come together behind their party's nominee.
Mr Obama has raised more than $7 million since Tuesday, boosting his already formidable financial advantage over Mrs Clinton, who disclosed this week that she lent her campaign $5 million last month.