The only mystery left in the Republican presidential race is guessing the moment when Rick Santorum bows to the inevitable. It may come with a gesture of face-saving capitulation before his home-state primary on April 24, with a feeling of forgotten-man frustration as Mitt Romney nears a delegate majority in early June, or with a final burst of angry defiance on the eve of the Tampa Convention. But whenever he bowls his last game on the campaign trail and fends off the last question about his illusory path to victory, I hope it will be remembered what Santorum single-handedly accomplished during sweater-vest season.

More than any presidential candidate since maybe Gary Hart in 1984, Santorum vindicated the quixotic dreamers who struggle on despite invisible poll ratings, tin-cup financing, and the dismissive wisecracks from political insiders. Santorum was a throw-back candidate—not only with his 1950s social values, but also in his forged-by-necessity embrace of the most old-fashioned way of running for president. In Iowa, where he made his move in the polls only two weeks before the January 3 caucuses, Santorum campaigned everywhere, responded at (sometimes tedious) length to every voter question, and cheerfully deflected skeptical press queries like the one I posed to him in mid-December: “Some days, don’t you get discouraged?”

What is already partially lost in the press coverage is how close Santorum came to stopping Romney—or, at least, sending the GOP race into overtime. After a miscount deprived Santorum of bragging rights as the winner of the Iowa caucuses, the former Pennsylvania senator blundered into New Hampshire (his first event was held in a nursing home) without a strategy for competing in a state with a negligible evangelical vote. Maybe if he had gone directly to South Carolina (65 percent of GOP primary voters said they were “born again” Christians), Santorum, rather than Newt Gingrich, would have been the beneficiary of the anti-Romney surge.

But still Santorum, fueled by his February caucus victories, came tantalizingly close to humiliating Romney in Michigan, the state where his father had been governor. Ohio was even closer. Just 42,000 votes—Romney’s victory margin in Michigan and Ohio combined—were all that Santorum needed for a plausible path to the nomination. But press coverage dwindled (unfairly in my book) after Romney swept Illinois—and Tuesday’s Wisconsin primary was the final straw.

Hogan Gidley, Santorum’s communications director, gamely argued in a phone interview Wednesday, “I’m not saying that if we win Pennsylvania and then Texas, we’re going to get to 1,144 votes and a convention majority. But if we win Pennsylvania and Texas, Romney won’t get to 1,144 either.” Gidley also floated the possibility of an overt alliance with Gingrich (the two anti-Romney candidates have spoken recently), but it is hard to see how that would make much difference. Santorum’s seemingly insurmountable problem is his inability to compete without debates; he just doesn’t have enough money to dominate the airwaves with a new anti-Romney argument and minimal press coverage. Even before his Wisconsin wipeout, Santorum had become an un-person on Fox News, the primary source of political information for GOP voters.

There is an argument, which I heard from Santorum allies, that the candidate should keep accumulating delegates in the remaining primaries, solely to strengthen his bargaining position in Tampa. The realism of that strategy may also have been a major topic of debate at a Thursday meeting that Santorum held with movement conservatives.

But to what end? Maybe it is possible for Romney to be bludgeoned into accepting Santorum as his vice-presidential running mate. There were ticket-balancing odd couples long before John McCain chose Sarah Palin. I can testify to the mutual loathing between John Kerry and John Edwards before they found themselves bound together on the 2004 ballot. Still, it seems implausible that Romney would choose to be weighed down with all the social-issue baggage that accompanies Santorum, at a time when the standard political technique is for the nominee to tap dance to the center for the general election. In short, Romney’s problems with social conservatives would have to reach the point of splitting the Republican Party asunder for Santorum to win the veepstakes.

Compared to the vice presidency, almost anything else that Romney could offer Santorum seems paltry. (Though the promise of a top foreign-policy post in a Romney administration might play to Santorum’s obsession with the Iranian nuclear threat.) Unlike Gingrich, Santorum does not appear to be saddled with the kind of campaign debt that would require the assistance of Romney fundraisers. About the only other coin of the realm in presidential politics is a primetime speaking slot at the GOP convention. Even that would be a bitter-sweet moment, since any advantage that Santorum might gain for a 2016 campaign (assuming Obama is reelected) would be counter-balanced by the slavish praise that he would be obligated to offer Romney as the party’s nominee.

The truth is that, in all likelihood, Santorum’s best hope in presidential politics died somewhere between Michigan and Ohio. With so many Republicans (Marco Rubio, please pick up the white courtesy phone) waiting for 2016, Santorum will probably never get another clear shot at the nomination. But as long as there are primaries and caucuses, as long as voters rather than party insiders choose presidential nominees, Rick Santorum should be hailed as the patron saint of underdog candidates. Not bad for a senator who was defeated for reelection in 2006 by 700,000 votes.

Walter Shapiro is a special correspondent for The New Republic. He also writes the “Character Sketch” column for Yahoo News. Follow him on twitter @waltershapiroPD.