Ron Paul, the US congressman who led a stubbornly persistent presidential bid against presumptive Republican nominee Mitt Romney and other rivals, says he is suspending active campaigning.
Paul said in a statement he will "no longer spend resources campaigning in primaries", opting instead to work on amassing delegates to the party's national convention, even though his chances of winning the nomination are virtually nil.
Paul insists his team "will continue to work in the state convention process" and seek to win delegates in order to "carry a strong message" to the Republican National Convention in Tampa, Florida in late August.
A Republican candidate needs 1144 delegates in order to be declared the nominee. Romney has some 949, according to a count by respected website RealClearPolitics, and is expected to wrap up the nomination on May 29 when he wins the Texas primary.
Romney's two main challengers, religious conservative Rick Santorum and former House speaker Newt Gingrich, dropped out in April and May, respectively, leaving Paul as Romney's lone Republican opponent for the past two weeks.
"This campaign fought hard and won electoral success that the talking heads and pundits never thought possible. But, this campaign is also about more than just the 2012 election," he said.
"It is about the campaign for liberty, which has taken a tremendous leap forward in this election and will continue to grow stronger in the future until we finally win."
After coming third in Iowa and second in New Hampshire - the first votes to choose the Republican who will challenge President Barack Obama in November - the unorthodox 76-year-old shot unexpectedly into the mainstream.
Few believed that Paul could parlay his support into enough delegates to win the nomination, but party elders have been careful not to trample his ideas in case he bolts altogether and launches a third-party presidential bid.