TAMPA — Isabella Santorum, the fragile 3-year-old daughter of Rick Santorum, has pulled through again.

She came down with pneumonia over the weekend, a frightening turn of events, given that Bella, as she is known, received a diagnosis of a fatal chromosomal disorder called Trisomy 18 shortly after her birth and has lived longer than most babies born with the illness. About two weeks after her birth, doctors sent her home from the hospital on hospice care, which is usually reserved for the end of life, not the beginning, saying that her condition was “incompatible with life.”

Bella’s condition is a constant challenge for the entire family, especially for Santorum’s wife, Karen, and their six other children.

But her health issues present another kind of challenge to Rick Santorum. As a presidential candidate, he is constantly traveling and must devote considerable time and energy to his campaign. Yet he is still a father. And ultimately voters may judge him on both of his roles — as a candidate and a parent.

“I think his priorities are right, if you have a sick child — whether you’re running for dog catcher or president of the United States — your family comes first,” said Gail Hebert, president of the St. Petersburg Republican Club in Florida.

By chance, Santorum was already with his family when he and his wife noticed that Bella had fallen ill; he had returned home from the campaign trail to retrieve his tax information.

But politically, the timing is awkward. Despite his surprise victory in the Jan. 3 Iowa caucuses, Santorum has not come close to winning anywhere else and is trailing badly in the polls here for the Florida primary today. He has been trying to beat back rumors that he is aiming for the vice presidential slot or that he will quit the race and urge his conservative supporters to back Newt Gingrich in an effort to stop the more moderate Mitt Romney.

To that end, his campaign moved quickly Sunday — even as Bella was still in the hospital and wearing an oxygen mask — to assure his donors and supporters that he was pressing ahead. In a conference call from her hospital room on Sunday night, Santorum said Bella had a “miraculous turnaround” and that he would rejoin the campaign trail Monday.

By Monday afternoon, he was in Missouri delivering an economic address and had planned other events and rallies in Minnesota, Colorado and Nevada through today.