(Image Credit: Paul J. Richards/AFP/Getty Images)

Analysis by Rick Klein

Leave it to Newt Gingrich, back in his role as strategist rather than candidate, to state the obvious reality of Mitt Romney's commanding position in the Republican presidential race.

"You have to be realistic," Gingrich said today on "Fox News Sunday. "He is far and away the most likely Republican nominee."

That matters almost not at all for Gingrich, whose campaign has morphed into an irregular traveling road show with a newly stated goal  of guarding against any Romney lurches toward the center, at the Republican National Convention and beyond.

But it should matter a great deal to Rick Santorum, who has more at stake in these next few weeks than any other Republican, up to and including Romney himself.

The hospitalization of Santorum's 3-year-old daughter, Bella, who suffers from a rare genetic disorder that's usually fatal in young children, has pulled the candidate off the campaign trail at least through Monday.

When he's able to return to campaigning, Santorum will have to decide whether he wants to. The primary in his home state of Pennsylvania looms just two weeks away, and Santorum will be risking much of what he's achieved in this campaign if he suffers an embarrassment there.

As for what he's risking, recall that few Republicans and fewer pundits thought much of it when Santorum announced his presidential candidacy. He then consistently registered approximately nowhere in the polls.

Santorum has shocked the political world by emerging as Romney's chief alternative. His slightly belated victory in Iowa was followed by a series of impressive showings, including wins in the Deep South and the Mountain West, and a blowout victory in Louisiana as late as March 24.

But even if he continues to surprise, he has fallen too far back in the delegate race to have a serious shot at capturing the nomination. He's secured only 281 delegates to Romney's 658, according to ABC News' delegate count; 1,144 are needed for the nomination, but only Romney has a legitimate mathematical shot of getting there, given proportional allocation rules in most states.

Santorum has labeled his home state a must-win. But even a win there would probably see him slipping further behind in the delegate race that day, because Romney-favored New York, Connecticut, Delaware and Rhode Island also vote April 24.

Nudging Santorum's decision-making along is Romney, whose campaign is pledging an ad buy of nearly $2 million, for starters, in Pennsylvania starting Monday. Polls have already begun to show Santorum's once-commanding lead there beginning to evaporate, and the Romney campaign has seen enough rivals get off the mat to let a chance to close out the race get away yet again.

Santorum has now gone from ex-senator who lost his last race in a landslide, to the silver medalist in a chaotic, once-crowded GOP primary. At 53, he's young enough to have a long future in the party, maybe even as a candidate again some day.

Romney's timely exit in his race against Sen. John McCain in 2008 has been widely cited as the first step toward what's on track to be a successful bid for the nomination in 2012.

For Santorum to follow a similar path, getting out on his own terms is a must. And losing on his own turf would hurt that prospect, perhaps beyond repair.