One Pennsylvania supporter, Chad Collie, said Santorum's withdrawal left him "speechless."
Collie, owner of a plaster and drywall business, had brought his wife and two children, ages 3 and 5, to what he expected to be a Gettysburg campaign event for the "truly genuine conservative" he planned to support in the state's GOP primary.
Would he be willing to vote for Romney instead? "We'll see," said Collie, who views Romney as about the same as Obama. "I'm not opposed to a third party."
Early on, Santorum wrestled with competing images: He was the sweater-vest-wearing, smiling underdog, a devoted father of seven taking on the Republican establishment and a multimillionaire front-runner. But he could also come across as a stern moralizer, worried that birth control was harming the nation and government-funded preschools were indoctrinating America's children into liberalism. He seemed to think working mothers would do better to quit their jobs and home-school their children, as his wife, Karen, did.
He called Obama "a snob" for wanting all Americans to have the opportunity to go to college. And he said fellow Roman Catholic John F. Kennedy's famous 1960 speech about the separation of church and state made him want to "throw up."
Republicans questioned whether Santorum could appeal to party moderates and independents — and female voters — if he were the party's nominee.
Santorum pointed to his four years in the House and 12 as a senator and argued that he had a stronger command of foreign and military affairs and the national economy than his opponents.
He reveled in his underdog status, reminding supporters that his campaign lacked the money and slickness of Romney's effort and that he spoke from the heart rather than prepared notes. At times, though, he appeared to talk himself into unnecessary controversies, as when he said the economy wasn't the race's top issue and unemployment didn't concern him as much as the federal government's threat against individual freedom.
Santorum did things the hard way, with relatively little money and scant campaign organization. At times on the campaign trail he bunked in a supporter's guest room.
Even his breakthrough win in the race's first contest, the Iowa caucuses, was bumpy.
Santorum, barely noticed amid a large, colorful Republican field, eked out a surprising victory over his better-funded opponents after doggedly holding 385 town hall meetings across the state. Initially Romney was declared the winner — by just eight votes — and Santorum was relegated to second place. But a few weeks later, the Iowa GOP sheepishly acknowledged errors in the balloting and declared Santorum the winner by 34 votes.
The delayed victory and a thinning field did little to help him in the next four states, where he typically finished in third or fourth place. Fundraising remained a problem, and Santorum was at times overwhelmed by the often negative TV ads supporting Romney.
Santorum's big night came Feb. 7, when he won all three of the states voting: caucuses in Colorado and Minnesota and a nonbinding primary in Missouri
Santorum and Romney tussled in a series of debates. Santorum tried to cast Romney as unable to challenge Obama on his health care law because of his support of a similar health care policy in Massachusetts. Yet Santorum stumbled — he was even booed — when he acknowledged during an Arizona debate that in Congress he had supported the No Child Left Behind law and other legislation he disagreed with because he had to support the overall Republican effort and "take one for the team."
As other candidates peaked and fell to the wayside, Santorum soldiered on to become the only realistic threat to Romney's ascension. Despite winning Super Tuesday contests in North Dakota, Oklahoma and Tennessee and later balloting in Kansas, Alabama, Mississippi and Louisiana, he kept falling further behind Romney in the delegate count. Santorum said he won 11 states "against all odds."