Four short months ago, Rick Santorum had hardly registered in national Republican presidential polls or made a blip in the candidate debates. People routinely asked whether he would drop out out of the race. Undaunted, he would reply that he was running the “Little Engine That Could” campaign.

But in what is perhaps the most astonishing turnaround of the 2012 political season, Santorum has, after 10 weeks of contests, all but claimed the title of leader of the conservative wing of the GOP — someone who deserves the right, at a minimum, to be a major player at the Republican National Convention and perhaps to be considered as a vice presidential nominee.

Like no other candidate, Santorum has used his presidential bid as a vehicle for resurrection and reinvention, erasing the taint of his 18-point loss for reelection to the Senate in 2006. He has almost certainly increased his market value along the way, giving him the chance to pursue the kind of lucrative path that accompanies national name recognition should he leave politics again.

Recently, Santorum has earned the trappings of campaign success, including a motorcade and his own theme song — great progress for a candidate who once showed up to events without a microphone or sound system.

More significant, with his victories in the deep South, Santorum has cemented his connection to the party’s base of social and religious conservatives, a group that has not always embraced Catholics but has found an unwavering standard-bearer in Santorum.

“At a minimum, he is going to be a significant conservative voice on the national political landscape,” conservative activist Ralph Reed said. “For a while, he was still kind of feeling his way to find the message that would click with the voters. You could see that he was trying out lines and he wasn’t quite there yet. But before this is over, he may well be president or vice president — and that is pretty remarkable for a defeated former senator who thought his career was over.”

Rival Mitt Romney has said that he would not pick Santorum as a vice presidential running mate, saying his fiscal record is not conservative enough. And Santorum, who is still running to be at the top of the ticket does not entertain the idea.

Yet, just as Hillary Rodham Clinton’s primary triumphs in 2008 led her supporters to clamor for her as Barack Obama’s vice presidential running mate, so, too, may there be a case for Santorum on a Romney ticket, if the former Massachusetts governor wins the nomination. The case for Santorum could be especially strong if he is perceived as able to unite the party base and drive up voter turnout.

“A lot of smart people make the case for Rubio and Christie being the future of the party, but Santorum is winning primaries today, and that has to count for something,” said Dan Schnur, who worked on Sen. John McCain’s White House bid in 2000, referring to Sen. Marco Rubio (Fla.) and New Jersey Gov. Chris Christie. “But until Romney finds a way to start convincing conservatives to vote for him, there’s no reason for Santorum to be thinking about a second spot on the ticket. It’s worth assuming that Rick Santorum went to bed Tuesday night thinking about who was going to be his running mate, rather than if he would be Romney’s.”

Although his shot at toppling Romney, who leads in the delegate count, remains a long one, Santorum has a passionate following among not only evangelicals but also blue-collar Republicans, who have powered him to wins in the South, the West and the Midwest, a streak that only he can claim.

He has demonstrated more staying power than multiple other former candidates, including Texas Gov. Rick Perry, Rep. Michele Bachmann (Minn.) and business executive Herman Cain. Santorum can now boast of having about 2.2 million voters and nearly 150,000 small donors — not to mention a television audience as a result of his near-daily hits on Fox News, where he had been a paid contributor but an infrequent guest.

Having pushed aside former House speaker Newt Gingrich (Ga.) by beating him in Mississippi and Alabama, Santorum is now refusing to cede any ground to Romney in the upcoming contests. Santorum campaigned in Puerto Rico on Thursday and plans to travel to Illinois.

Santorum’s campaign apparatus these days is lean — no campaign plane, no big advance staff. But he has moved beyond the days when his oldest daughter was in charge of the research for getting on ballots in all 50 states and when his supporters stuffed donations into an aide’s manila envelope.

As Republicans size up their chances to beat President Obama, Romney’s continued inability to connect with conservatives remains a challenge. If Romney is the nominee, having Santorum as a running mate could help boost excitement among lower-income voters and evangelicals.

Yet in 2008, McCain’s choice of Alaska Gov. Sarah Palin was an attempt to address a similar problem — one with ultimately disappointing results.

In other ways, Santorum has picked up where former Arkansas governor Mike Huckabee left off, scooping up not only several of his former aides but also borrowing his one-state strategy in Iowa, and using his victory there to fuel his campaign and lift his national profile.

When the campaign ended, Huckabee landed a lucrative deal at Fox News, a path that Santorum, who has a sort of aw-shucks charisma, could also possibly take.

“His name has become prominent, everyone recognizes who he is, he has a base that constitutes a significant audience for television, and he is a young man and he could run again,” said Robert Thompson, the founding director of the Bleier Center for Television and Popular Culture at Syracuse University. “It’s not like he is going to get the leading role in a new Whitney Cummings sitcom, and I can’t imagine him having something like Sarah Palin’s reality show. But these days, one never knows, given how far he’s gotten into this wild GOP primary period.”

Staff writer Rosalind S. Helderman contributed to this report.