Rick Santorum, who ended his race for the White House Tuesday, emerged as an improbable contender for the Republican nomination, with a faith-and-family message that caught fire with the party's most conservative voters.

Even as he quit the rollercoaster Republican presidential race, he remained the candidate who seemed to stir the fiercest reactions with his radical views on religion, women and marriage.

His dark horse presidential bid had turned into a surprisingly strong challenge to Mitt Romney, long considered the frontrunner but who faced a succession of challengers nipping at his heels.

"This presidential race is over for me," Santorum, a former US senator told a hastily convened press conference in Gettysburg, Pennsylvania.

Santorum now leaves a clear path to the nomination for Romney, the former Massachusetts governor, who is all but assured of becoming the Republican nominee to challenge President Barack Obama in November.

As he bowed out of the race Tuesday, Santorum said during his campaign: "I found a deeper love for this country. I traveled around, it was a love affair for me going from state to state... seeing the wonderful, wonderful people of this country who care deeply about where this country is going."

But he faced the ignominious prospect of possible defeat in his home state of Pennsylvania, which holds its presidential primary on April 24.

Despite his staid knitted sweater vest and easy boyish smile, Santorum was given to passionate outbursts about God and country which endeared him to right-wing conservatives.

But those same strong conservative views, born from his Catholic faith, had given many pause.

A virtual unknown when he first threw his hat into the ring in June, Santorum, 53, built his campaign state-by-state -- a David and Goliath struggle against the Romney juggernaut powered by a huge warchest and a solid organizational machine.

Santorum's pro-life, marriage-only-between-a-man-and-a-woman and anti-contraception message had gained traction with heartland evangelicals deeply skeptical of Romney, whom they view as a moderate disguised in conservative clothing.

Yet on the other end of the spectrum, critics saw his radical right-wing views as scary. A website called "Santorum exposed" said it was dedicated to "shining a bright light" on what it calls the former senator's "extreme positions."

Santorum, a global warming skeptic, has called Obama "a snob" because he believes all kids should have a college education, and said he wanted "to throw up" when watching beloved former president John F. Kennedy talk about separation of church and state.

"I don't believe in an America where the separation of church and state is absolute," he told US television recently.

At a campaign stop in Ohio earlier this year, Santorum also hit out at Obama saying the president's "world view" elevated the Earth above man.

"That's what I was talking about -- energy: this idea that man is here to serve the Earth, as opposed to husband its resources and be good stewards of the Earth. And I think that is a phony ideal."

Asked to define himself in one word at a recent debate, Santorum replied "courage." That steely resolve, refusing to stray off his message of "Family, Faith and Freedom," defined his campaign even as it struggled.

A trained lawyer and father of seven who has been married to his wife Karen for 21 years, Santorum was first elected to the House of Representatives from Pennsylvania in 1990. He served two terms in the US Senate from 1995 to 2007.

Santorum has often spoken of his seriously ill youngest daughter, Bella, who suffers from a genetic disorder, trisomy 18 -- or Edwards syndrome.

He had to break away from the campaign in January and again over the weekend to be by her bedside as the three-year-old recovered from treatment.

Although she is now home fighting pneumonia, Santorum said the family had spent a difficult few days which had given them cause for reflection.

In the past, he has also tearfully recounted a family tragedy in 1996 when a son died hours after being born prematurely. He and his wife spent the night with the body and brought it home to show to their other children before burying it.