Washington: Ending month long speculation, US Presidential candidate nominee, Rick Santorum on Tuesday quits, after leading a Republican tilt to the right that could dog the more moderate front-runner, Mitt Romney, in November's election.

Trailing in polls and fundraising, the conservative former senator suspended his campaign and cleared the way for Romney to clinch the nomination to face President Barack Obama in the November 6 general election.

A staunch social conservative with a penchant for sweater vests, Santorum was the underdog who clawed his way to near the top of the Republican race and won the first 2012 nominating contest in Iowa by a whisker.

Santorum as Romney’s opponent

His rise forced the issues of birth control and the role of Christianity in public life to the forefront of the campaign, when former executive Romney sought to focus on the economy.

"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," Santorum said at a news conference in 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 historic 18-percentage point defeat in his Senate re-election bid in 2006.

Issues raised by Santorum in campaign

His strong opposition to gay marriage and abortion offered Republican voters a stark contrast with Romney's more moderate record.

Romney moved to the right on social issues to try to outflank Santorum but that leaves him, and Republican congressional candidates, exposed in November when the electorate will be more moderate.

"When voters are interested in the economy, Rick Santorum was talking about socially conservative issues ... and that would take us off message. That would take the whole party off message," said Republican strategist Ron Bonjean.

Santorum lagged 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 clears way for Romney

Santorum spoke to his main rival 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.

"Mr. Santorum brought excitement to the race, and helped the GOP mobilize 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. Disappointed Santorum supporter Felicia Collie, 29, of Gettysburg, wasn't ready to throw her vote to Romney.

"I don't really want to because Romney is the same as Obama," she said. "Santorum is the only one (of the Republican candidates) who is a clear contrast."

(JPN/Agencies)