After calling Mitt Romney to concede the race for the Republican nomination, Rick Santorum suspended his campaign Tuesday during a press conference in Pennsylvania, his home state.

"We will suspend our campaign effective today," Santorum said, surrounded by members of his family in Gettysburg.

Santorum spent the weekend off the campaign trail with his 3-year-old daughter, Bella, who suffers from a rare genetic disorder, after she was rushed to the hospital Friday.

"We made a decision over the weekend that, while this presidential race for us is over, for me, and we will suspend our campaign effective today, we are not done fighting," he said.

At a campaign event in Delaware on Tuesday, Romney spoke about his phone conversation with Santorum earlier in the day.

"We both have a great deal of interest in seeing the country taken on a very different path," Romney said. "I look forward to his work in helping assure victories for Republicans across the country in November."

Few thought Santorum would make it this far.

The former Pennsylvania senator spent most of 2011 on a grueling and often lonely campaign tour through Iowa. His strenuous underdog campaign was organized by a skeleton staff and run the old-fashioned way: by methodically speaking with voters face-to-face, town by town. Candidates like Michele Bachmann, Rick Perry and Herman Cain rose and fell throughout 2011, while Santorum spent the year mostly relegated to the far end of the debate stage. He was a long-dormant volcano due for a surprise eruption.

In the final days before the first Republican caucuses in Iowa—a contest on which Santorum rested his entire strategy—it appeared that his campaign would be laid to rest in the state where it was born. Iowa Republicans did not turn their eyes to the man who had spent more time in their state than any other candidate until the very end, but they ultimately awarded him with a surprise, hair's-breadth victory—not formally confirmed until weeks after the vote—that helped keep his fledgling campaign afloat into the spring.

Story continues

The first public whispers of his impending rise came with a CNN poll released three days after Christmas that showed Santorum in third place among likely Iowa caucus-goers, higher than he had ever been before in a public opinion survey. When CNN first announced the poll, Santorum was greeting a small group of supporters at a furniture store in Dubuque. As he weaved between La-Z-Boy recliners and leather couches, a reporter showed Santorum the poll results on her BlackBerry. Santorum paused and read the results. While composed, his face revealed an expression of shock mixed with relief.

"I feel very, very good about how things are going, and it's nice to see that reflected in some of the polls," Santorum said after surveying the good news on the reporter's phone. "But we have a lot of work to do. A lot of work."

Before the good polls began to pour in, it was not entirely uncommon for Santorum to hold town halls in which only a handful of supporters bothered to show up. The heart of Santorum's Iowa support rested in the deep red northwest corner of the state, a solid four-hour drive from Des Moines, where many reporters made their home base. At the time, driving all the way to the South Dakota border to see the candidate, even when no other candidates were in the state, didn't seem worth the effort. "I'd usually make the drive to see a candidate," one reporter, comfortably nursing a beer at a Des Moines hotel bar, said in early December. "But it's Santorum."

By New Year's Eve, when a Des Moines Register poll showed Santorum gaining swift momentum, the grim outlook among reporters covering his campaign would change. In the final days before the caucuses, if you arrived on time for an event, you'd be stuck outside in the cold. Every pizza place, coffee shop and diner Santorum visited was jam-packed with supporters, media and curiosity seekers, sometimes hours before his arrival.

For the first time in the entire cycle, Romney turned his gaze to Santorum, about whom the Romney campaign didn't even bother to collect early opposition research, according to a report published much later by Politico. Romney criticized Santorum on the stump during a New Year's Day rally for spending 16 years in Washington in the House and Senate, one of the first times Romney took time out of his stump speech to discuss Santorum.

"I think it shows that we're on the move," Santorum said in response. "And we're resonating with the people of this state."

He was right. While an initial count of Iowa votes showed Romney winning by a mere eight votes, the final results—released several weeks later during the South Carolina primaries, a scenario that robbed Santorum of the boost in news coverage that traditionally comes from winning the Iowa caucuses—put Santorum over the top by 34 votes.

"This is a solid win," Santorum said during a stop in South Carolina two weeks after the Iowa caucuses. "It's a much stronger win than the win Gov. Romney claimed to have."

Over the next few contests, Santorum took a backseat role to former House Speaker Newt Gingrich, who defeated Romney in South Carolina before Romney scored a win in Florida. Dogged by an aggressive series of attack ads run by the Romney campaign in Florida, Gingrich's momentum slowed after South Carolina, leaving the door open for Santorum to take his position as the alternative candidate to the former Massachusetts governor. Against most predictions, Santorum swept a three-state contest on Feb. 7, winning caucuses in Colorado and Minnesota and a nonbinding primary in Missouri.

Santorum was back on the map and would remain Romney's greatest challenger for the remainder of the race.

Over the next two months, Santorum would go on to win only a handful of states, as Romney increased his delegate lead. By the time Romney won a majority of votes in the Wisconsin primary on April 3, most observers within the party and in the media declared an end to the Republican primary cycle. Romney would take it, they predicted. But with his home state looming just three weeks away, Santorum vowed to press on.

"If this thing was all about D.C. pressure for us to get out, we'd have never even set foot in Iowa," Santorum spokesman Hogan Gidley told reporters the night Romney swept contests in Wisconsin, Maryland and the District of Columbia. "This thing's been going on for a long time. We're not worried at all about the pressure we're going to get from the outside D.C. world, we've had it from the get-go."

While Santorum voiced confidence that he would win Pennsylvania, where he lost his Senate seat in 2006 to Bob Casey by the record margin of 18 percentage points, state polls leading up to the primary date showed momentum to be on Romney's side.

"I walked out after the Iowa caucus victory and said 'game on,'" Santorum said in Gettysburg. "I know a lot of folks are going to write—maybe even those at the White House —'game over.' But this game is a long, long, long way from over. We are going to continue to go out there and fight to make sure that we defeat President Barack Obama."

More popular Yahoo! News stories:

• How to predict Mitt Romney's running mate

• Women boost Obama over Romney in new ABC poll

• North Korea rocket 'propaganda' condemned by White House

Want more of our best political stories? Visit The Ticket or connect with us on Facebook, follow us on Twitter, or add us on Tumblr. Handy with a camera? Join our Election 2012 Flickr group to submit your photos of the campaign in action.