Conservative Rick Santorum dropped out of the presidential race on Tuesday, clearing the way for former Massachusetts governor Mitt Romney to clinch the Republican nomination.     

Trailing Romney in opinion polls and fundraising, the former senator from Pennsylvania told reporters he was suspending his campaign. That effectively ends his bid to be the Republican who will face President Barack Obama in the November 6 general election.     

A staunch social conservative, Santorum was an underdog who clawed his way to near the top of the Republican race and won the first nominating contest in Iowa by a whisker. His influence forced the issues of birth control and the role of Christianity in public life to the forefront of the campaign.       

'Over and over again we were told 'Forget it, you can't win.' We were winning, but in a different way, we were touching hearts, we were raising issues that frankly a lot of people didn't want to have raised,' he said at a news conference at a hotel near the Civil War battlefield site of Gettysburg.           

Santorum proved to be a more formidable opponent to Romney than many expected, especially in light of a stinging defeat in his Senate re-election bid in 2006. His conservative appeal offered voters a stark contrast with Romney's more moderate record.     

Santorum was lagging Romney in opinion polls and in the fight for the 1,144 party delegates needed to win the nomination. He was facing the possibility of an embarrassing defeat in his home state of Pennsylvania on April 24.     

A devout Catholic with seven children, Santorum failed to stretch his appeal far enough beyond conservatives and some blue-collar Republicans to be able to overtake Romney.        

Santorum spoke to Romney on Tuesday but did not announce an endorsement of the front-runner or either of the other two Republican candidates, Ron Paul and Newt Gingrich, both of whom are way behind Romney in polls.     

'Santorum brought excitement to the race, and helped the GOP mobilise voters earlier in the season. Now much of the electorate will tune out until the fall. His delegates will now be open at the convention, but will likely support Mitt Romney,' Hunter College Political Science Professor Jamie Chandler said. - Reuters