By Catalina Camia and Jackie Kucinich

USA TODAY

Updated 4:08 p.m. ET

Rick Santorum suspended his campaign for the GOP presidential nomination, effectively giving Mitt Romney a clear path to be the party's standard-bearer.

Santorum made his announcement in Gettysburg, Pa., just two weeks before the Keystone State primary. Recent Pennsylvania polls had Santorum in danger of losing the state where he was a senator for 12 years.

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"We made the decision over the weekend that while this presidential race is over for me, and we will suspend our campaign effective today, we are not done fighting," Santorum said. "We're going to continue to fight for the Americans who stood up and gave us that air under our wings that allowed us to accomplish things that no political expert would have expected."

Santorum did not mention Romney in his remarks, but said America needs "leaders ... who are willing to give voice" to the greatness of the country and "willing to rise us up instead of trying to provide for us."

"This game is a long, long, long way from over," he said. "We are going to continue to go out there and fight to make sure that we defeat President Barack Obama, that we win the House back and that we take the United States Senate."

By suspending his campaign, Santorum will no longer be actively running for the White House. But he will be able to continue raising money for his political activities through the political action committee he launched for the 2012 election. Santorum immediately sent out a fundraising appeal, asking donors to help reduce his campaign debt.

Shortly after Santorum's news conference, Romney issued a statement hailing his rival as "an able and worthy competitor, and I congratulate him on the campaign he ran."

"He has proven himself to be an important voice in our party and in the nation," Romney said. "We both recognize that what is most important is putting the failures of the last three years behind us and setting America back on the path to prosperity."

Santorum opened his news conference by thanking people for their prayers for his youngest daughter, Bella, who was hospitalized on Friday and released last night.

Her condition "caused us to think ... about the role we have as parents," Santorum said, adding that the weekend was a time for "prayer and thought" about his future.

Before the news conference, Santorum's campaign was tight-lipped about the candidate's future. There were signs, however, that the end could be coming. The conference room reserved for the event was small and there were last-minute cancellations of other events in the state.

Santorum's decision marks the end of an unpredictable ride for the former Pennsylvania senator, who was seen as having little chance for the White House more than a year ago when he launched his bid.

Despite primary victories in several states, Santorum has been unable to translate votes from Tea Party members, the most conservative voters, and evangelicals into a coalition that could sustain him.

Long a favorite of social conservatives, Santorum appealed to voters with his view that the federal government under Obama was trampling on people's rights -- whether through the national health care law or a proposed rule that would have required religious institutions to provide access to contraceptives.

He and Newt Gingrich were viewed as competing for the same voters, but Santorum in recent weeks ignored the former House speaker as he pushed his campaign as being the "consistent conservative" alternative to Romney.

Santorum's rise to the final four GOP presidential candidates was unlikely, especially because he had lost his 2006 re-election bid as a Pennsylvania senator by more than 17 percentage points.

Despite being underfunded and in low single-digits in most national polls for much of 2011, Santorum concentrated on meeting Iowa voters in small groups so he could do well in the first-in-the-nation caucuses. His surprise showing in Iowa -- after weeks of vote counting he was declared the winner by a tiny margin -- positioned him as a viable candidate, and the sweater vests that he wore while campaigning became a symbol of his success.

A few weeks later, Santorum scored a surprise political hat trick, winning the caucuses in Colorado, Minnesota and Missouri. It was a blow for Romney, who had invested time on the ground and on the airwaves in Colorado and Minnesota.

Santorum, however, was later outgunned by the better-funded Romney and the super PAC supporting the former Massachusetts governor in key battleground states such as Ohio and Michigan. Despite recent victories in Alabama, Mississippi and Louisiana, Santorum has been unable to gain much on Romney's big lead in the delegates needed for the GOP nomination.

At times, Santorum was derailed at critical junctures in the campaign by his own remarks. Before the Michigan primary, it was his comment that President Obama is a "snob" for wanting "everybody to go to college." Ahead of the Illinois primary, Santorum said he didn't care about the unemployment rate. In March, Santorum had to explain that he would vote for the GOP nominee after suggesting Obama would be a better choice than Romney.

Santorum's wife, Karen, and the couple's older children were ever-present on the campaign trail and at election-night parties. Santorum suspended campaigning at least three times since last year because of Bella's health, including most recently this weekend.

Bella, now 3 years old, suffers from trisomy 18, a rare genetic disorder. Also known as Edwards syndrome, trisomy 18 is caused by the presence of all or part of an extra 18th chromosome. There is a low rate of survival, and Santorum has often talked about how Bella was not expected to live past her 1st birthday.