In one sense, Rick Santorum took the first step in the unpredictable journey that ended Tuesday back on Nov. 7, 2006.
That was the day that his congressional and, seemingly, his political career was interred beneath Democratic Pennsylvania Sen. Bob Casey's landslide victory. Six years later, Mr. Santorum's longtime political adviser, John Brabender, remembered the bleaker news of that night as he exulted with the former Republican senator over his startling finish in January's Iowa caucuses. Mr. Santorum actually had won the kickoff event to the GOP's nomination, but the finish was so close that no one would know that until weeks later.
"Miracle after miracle," Mr. Santorum said Tuesday in his withdrawal speech in Gettysburg, "this race was as improbable as any you will see for president."
In the years after his Senate defeat, Mr. Santorum had settled into a typical post-congressional career of speechmaking, consulting -- none dare call it lobbying -- and public commentary. But the health care debate, the tea party-led Republican congressional gains of 2010 and his personal ambition -- which had led him, when he was just 32, to challenge an entrenched Democratic House member -- once again pushed him to defy the odds.
Through late 2010 and early 2011, Mr. Santorum made forays into Iowa, New Hampshire and South Carolina, earning little attention and occasional derision from voters and commentators who would be gatekeepers of the Republican competition. But he remained convinced that the GOP primary path through Iowa blazed four years earlier by former Arkansas Gov. Mike Huckabee through the networked worlds of social conservatives and home-schoolers would lead to his relevance in the White House race.
On the presidential primary trail, the core of Mr. Santorum's support was formed by voters attracted by his long-held conservative stands on abortion and other social issues.
Against long odds and a massive spending imbalance, he amassed a remarkable string of victories.
But despite strong showings in big states such as Michigan and Ohio, he was never able to break through to a victory in any state that did not have a heavy proportion of evangelical Christian voters. A devout Roman Catholic himself, he had less success with Catholic voters, and former Massachusetts Gov. Mitt Romney, a Mormon, consistently bested him among mainline Protestants.
Through most of last year, Chuck Laudner, a former Iowa Republican Party executive director, was his truck chauffeur, as they visited each of Iowa's 99 counties for usually low-key events at county GOP dinners and Pizza Ranch restaurants. As rivals concentrated on televised debates that punctuated the race, Mr. Santorum, making a virtue of necessity, focused on a low-budget shoe leather campaign.
He remained mired in single digits well into the fall, never threatening to join the revolving parade of Republican front-runners.
In August, in the Iowa Republican straw poll, a third-place finish drove former Minnesota Gov. Tim Pawlenty from the race, but expectations for Mr. Santorum were so low that his fourth-place showing was considered a surprising boost to his campaign.
In the final days before the Iowa caucuses, Bob Vander Plaats, president of The Family Leader, a prominent evangelical Christian and a former Iowa gubernatorial candidate, endorsed Mr. Santorum -- news that symbolized and accelerated the move toward him among social conservatives, who had been casting around for months seeking an alternative to front-running Mr. Romney.
Still, days before the caucuses, Mr. Santorum's polling support was creeping only into the teens. So his reported second-place caucuses showing brought surprise and elation to the suburban Des Moines motel where Mr. Santorum and his supporters awaited the returns.
After a tense night of back-and-forth counting, second place to the much-better-funded Mr. Romney seemed more than good enough. But an embarrassed Iowa GOP later would admit that a more complete count showed that Mr. Santorum won the party contest by 34 votes, rather than trailing by eight, as first reported.
Mr. Santorum will never know whether an accurate report of that victory would have given him more momentum out of Iowa. But even in second place, he was the big story. Aides argued that a timely recognition of his win would have helped fund-raising, always a vulnerability, and given him earlier title as the field's anti-Romney, the candidate able to unite conservatives wary of the former governor.
In New Hampshire, where Mr. Santorum wasn't able to capitalize on his Iowa showing, former House Speaker Newt Gingrich of Georgia attracted headlines with his populist attacks on the Romney business record. In South Carolina, Mr. Gingrich won his first victory after a high-profile debate clash with a CNN anchor.
The day of that debate encapsulated the difficulty Mr. Santorum continued to have in breaking to the contest's front rank. The political world was aswirl with gossip about an interview Mr. Gingrich's ex-wife gave, in which she depicted Mr. Gingrich as an advocate of "open marriage." Brushing aside the controversy, Mr. Perry ended his campaign and endorsed the former speaker hours before the debate. At the same time, the Iowa GOP announced that its subsequent count of that state's vote had gone in Mr. Santorum's favor. But news of the true Iowa result had to compete for second or third place in that day's political news.
If there was consolation for Mr. Santorum, it was that he still had a smaller target on his back. Mr. Gingrich bore the full brunt of the Romney assault in Florida's expensive primary, where Mr. Santorum invested few resources beyond his well-reviewed performances in two debates.
But within days of Mr. Romney's commanding win in Florida, Mr. Santorum re-emerged as a serious threat with a Feb. 8 sweep of three states: Missouri, Minnesota and Colorado. Continuing to trail Mr. Romney in delegates, he won three more states March 6, Super Tuesday, and moved into Michigan, Mr. Romney's birth state, with new momentum and a lead in an least one pre-primary poll.
But the confident, confrontational Mr. Santorum slowed his new momentum controversial public observations that President Barack Obama was "a snob" for advocating universal college education, and that a 50-year-old speech by the late President John F. Kennedy about separation of church and state had made him want "to throw up."
Even as Mr. Santorum and other Republicans were trying to put the White House on the defensive over its controversial health care law demanding that some religious institutions provide coverage for contraception, Mr. Santorum helped sidetrack news coverage with his unapologetic personal opposition to contraception. He lost Michigan narrowly. After another close Romney victory, the next week in Ohio, the race seemed sealed.
Yet Mr. Santorum battled on, resisting Mr. Romney's continuing efforts to paint him a creature of the discredited Washington GOP establishment and a congressional advocate of earmarks and union-friendly legislation. Mr. Santorum didn't need any encouragement to fire back. While he said he wouldn't rule out an offer, it seemed clear that he wasn't running for vice president, as he relentlessly portrayed Mr. Romney as an untrustworthy advocate of policies, such as the Massachusetts health care law he signed as governor, that would make him a fatally weak presidential nominee.
Coming into Pennsylvania, Mr. Santorum argued that a win in his own state could sustain him until the campaign reached friendlier territory in a string of Southern contests in May. But his poll numbers weakened, even among his former constituents. Several surveys showed a narrow lead among Pennsylvania Republicans, while one actually found Mr. Romney ahead. The challenger was facinig a prospect of adding a 2012 primary loss to his 2006 general election landslide defeat.
Mr. Santorum said the family's kitchen table deliberations were influenced by the fact that their 3-year-old daughter, Bella, who suffers from a genetic disorder, Trisomy 18, had been hospitalized over the Easter weekend, though since released.
Mr. Brabender told reporters that his candidate and Mr. Romney spoke Tuesday. Despite his harsh attacks on the presumed GOP nominee, Mr. Santorum has also said repeatedly that he and other Republicans would have no trouble uniting in opposition to Mr. Obama.
After the campaign's vitriol, it would be a surprise if that unity extended so far as a vice-presidential nomination. But after a campaign that lifted him from the status of political has-been to his party's front ranks, Mr. Santorum is certain to be included in conversations about future races.
Politics editor James O'Toole: firstname.lastname@example.org or 412-263-1562.