For Santorum, new challenges follow his big wins

Speaking to a small audience of employees at a Jergens metal manufacturing plan in Cleveland, Gingrich said the United States could pay a terrible price if Iran develops nuclear weapons.

"Remember what it felt like on 9/11 when 3,100 Americans were killed. Now imagine an attack where you add two zeros. And it's 300,000 dead. Maybe a half million wounded," he said.

This is not the first time Santorum has awakened to new campaign energy in the 2012 race, and he is not the only contender to have the experience.

He appeared to finish a surprising second in the lead-off Iowa caucuses a month ago, then sank in New Hampshire's primary a week later and seemed to disappear.

Gingrich, too, was the candidate on a roll after he stunned Romney with a double-digit victory in South Carolina on Jan. 21. He was buried in Florida 10 days later under an avalanche of attack ads from Romney and Restore Our Future, an organization that supports him.

Taking note of Santorum's triumphs on Wednesday, Gingrich said the party could convene next summer without any candidate in control, the first that would have happened since 1940.

In a fundraising letter to supporters, Santorum appealed to conservatives and — in a jab at Gingrich — likened his situation to the one Ronald Reagan encountered in 1976 when he challenged President Gerald R. Ford for the GOP nomination.

Reagan lost the first eight primaries, Santorum wrote, and "the media and the establishment made fun of his campaign; they said he had no shot, and told him to get out of the race." But then he won several states and carried his campaign into the convention, where he ultimately lost.

Associated Press writers Charles Babington in Cleveland, Phillip Elliott and Stephen Ohlemacher in Washington and Steve Peoples in Atlanta contributed to this story.