Just off Highway 17 in the Charleston suburb of Mount Pleasant, South Carolina, we found the shopping center where the state campaign headquarters was located. It was Tuesday, Jan. 17, and my 13-year-old son Jefferson was along for the ride on my road trip to cover the South Carolina primary. The day before in Myrtle Beach, Jefferson had helped me cover the press conference where former Utah Gov. Jon Huntsman announced he was ending his presidential bid and endorsing former Massachusetts Gov. Mitt Romney. Then, that Monday night, we’d covered the Fox News debate that was generally acknowledged as a solid win for former House Speaker Newt Gingrich.

We hadn’t come to the Palmetto State to cover Gingrich, Romney or Huntsman, however, and so on that Tuesday afternoon, driving from Myrtle Beach to Charleston, we pulled off Highway 17 in Mount Pleasant to visit Rick Santorum’s South Carolina headquarters. Wheeling into the parking lot, I spotted two familiar-looking young men walking out of the office, carrying large boxes. Rolling down my window, I asked, “Where y’all heading?”

“Mail drop,” said John Santorum, eldest son of the candidate, as he and his younger brother Daniel loaded the boxes into an SUV and drove off to the local post office.

Lots of Republicans talk about “family values,” but the Santorum campaign could never have made it as far as it did without the valuable work done by the candidate’s wife, Karen, and their children. During the long months when the former Pennsylvania senator struggled to raise money and media attention, Santorum’s wife and kids were among the campaign’s hardest-working volunteers. They made phone calls and stuffed envelopes and did the work that other campaigns paid staffers to do. The first time I covered Santorum’s campaign — at a barn party in Roland, Iowa, a week before the Ames Straw Poll — his daughters were serving ice cream to the few dozen supporters in attendance. On that first Saturday in August, Santorum was below 4 percent in the Real Clear Politics average of Iowa polls, and his national poll numbers were so low, he barely qualified to participate in the early debates.

Among the candidates leading Santorum in the polls at the time, former Minnesota Gov. Tim Pawlenty was destined to quit eight days later, after a disappointing third-place finish at Ames. The winner of the Aug. 13 straw poll, Minnesota Rep. Michelle Bachmann, ended her campaign on Jan. 4, the day after she placed sixth in the Iowa caucuses. Atlanta businessman Herman Cain, who placed fifth in the Ames Straw Poll, eventually called it quits in early December, and Texas Gov. Rick Perry — whose official entry into the 2012 Republican field on Aug. 13 made him a front-runner overnight — raised and spent more than $19 million in a campaign that earned him fifth place in the Iowa caucuses and sixth in the Jan. 10 New Hampshire primary before calling it quits two days before the Jan. 21 primary in South Carolina. Santorum’s campaign raised just $2.2 million in all of 2011; by the time he emerged as one of the final four candidates for the GOP nomination, he had outlasted five candidates — Pawlenty, Cain, Bachmann, Huntsman, and Perry — all of whom once led him in the polls, and whose campaigns spent a combined total of more than $55 million.

Santorum’s low-budget campaign accomplished miracles, beating Romney in 11 states, and topping Gingrich in all but two states, South Carolina and Georgia. Yet by the time the campaign trail brought Santorum home to Pennsylvania, Romney’s overwhelming delegate advantage left Santorum little hope that he could win the nomination. The Romney operation had already launched another one of its multimillion-dollar attack-ad blitzes in Pennsylvania and the experts — who had never expected Santorum to make it this far — were finally right in predicting that he could go no further. Faced with the prospect of almost certain defeat in his home-state primary on April 24, Santorum went to Gettysburg and gave one of the best speeches of his entire campaign, praising the youngest member of his family, 3-year-old daughter Bella.

“She is a fighter,” Santorum said of the little girl, born with a rare and usually fatal genetic disorder, who had just been released from the hospital for the second time this year. As his wife stood behind him, struggling to hold back tears, Santorum continued: “This was a time for prayer and thought for us over this past weekend and just like it was, frankly, when we decided to get into this race. Karen and I and the kids sat at the kitchen table and talked about our hopes and fears and our concerns. We were very concerned about being the best parents we could possibly be to our children, and making sure they had a country where the American dream was still possible.… We started out, almost a year ago now, in Somerset, in Pennsylvania, and I told my story, our story, of our family — my grandfather who came to this country and worked in the coal mines, my father who served our country in World War II.”

Santorum continued, telling the story of the “Chuck Truck” — a Dodge pickup driven by Chuck Laudner, an Iowa Republican who crisscrossed the Hawkeye State with a candidate none of the experts gave a chance. “Over and over again, we were told, ‘Forget it, you can’t win,'” Santorum recalled in his final campaign speech. “We were winning. We were winning in a very different way. We were touching hearts. We were raising issues that, well, frankly, a lot of people didn’t want to have raised.”

Ah, yes, the “social issues” — none of the experts wanted to hear about abortion and marriage and other things that Santorum talked about. Just eight years ago, when President Bush was re-elected, the pundits proclaimed that “values voters” had been the key to Republican success. But 2012, the pundits said, the Republican campaign would be all about the economy, with as little attention as possible to the kind of issues that made Santorum such an unexpectedly successful contender.

His teenage sons were still doing mail-drop duty that January day my son and I arrived at Santorum’s South Carolina headquarters. At that point, everyone still believed that Romney had squeaked to a narrow victory in Iowa. It wasn’t until two days before the South Carolina primary that a recount showed Santorum had won the Hawkeye State, but that news made little impact at a time when the campaign seemed to have become a two-man race between Romney and Gingrich. Santorum and his family kept fighting. After Newt stumbled in Florida and Nevada, Santorum scored surprising victories Feb. 7 in Colorado, Minnesota, and Missouri, won Tennessee, Oklahoma, and North Dakota on March 6, Kansas on March 10, Missouri and Alabama on March 13, and Louisiana on March 24.

Now, back home in Pennsylvania, his improbable success having carried him farther than anyone imagined during those months when he was riding around Iowa in the “Chuck Truck,” Santorum reached the end of the campaign trail.

“We made a decision over the weekend that… this presidential race for us is over, for me,” he said Tuesday. With his family standing behind him, Santorum made a final vow. “We are not done fighting.”