Rick Santorum suspended his campaign Tuesday afternoon, clearing the path for his rival Mitt Romney to become the nominee.
Santorum said he and his family had made the decision over the weekend after his 3-year-old daughter's latest hospitalization.
Romney congratulated Santorum on his campaign, calling him an "able and worthy competitor."
It was the expected end to an improbable candidate. Santorum had a fraction of Romney's money and in some states a non-existent ground game. Still, he managed to win 11 states and millions of votes, but not enough to put a wrench in Romney's well-oiled machine.
"While this presidential race for us is over -- for me -- and we will suspend our campaign effective today, we are not done fighting," said Santorum.
Rick Santorum's battle for the Republican nomination ended in Gettysburg, Pennsylvania.
"I know a lot of people will write -- some even in the White House -- that it's game over," Santorum said. "But this game is a long, long way from over."
Santorum promises to continue to fight to make Barack Obama a one-term president.
And, that includes supporting Mitt Romney. The two talked by phone Tuesday. Then Romney released a statement, saying, "Senator Santorum is 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."
Newt Gingrich was less gracious. He said, "We had the Santorum surge... I said at the time, 'Oh yeah, this is the new one.' Well, if in fact he's getting out today, we've now survived that surge."
"It just got the point where the math just was not going to add up for us," said Santorum's Illinois state chairman Al Salvi.
Already, Santorum supporters in Illinois are lining up with Romney while still taking stock of Santorum's unlikely surge.
""I think the legacy is, even in 2012, you can get a guy in a truck and travel around Iowa and be under 1 percent in the polls and still have a shot at being a major party's candidate for president of the United States," said Salvi.
Santorum decided to get out of the race as polls showed his gap with Romney was only increasing, even in Santorum's home state of Pennsylvania, which has its primary later this month.
Over the weekend, Santorum's daughter Bella, who suffers from a rare genetic disorder, was hospitalized for the second time in recent weeks.
"She is a fighter, and she is doing exceptionally well and is back with us and the family," said Santorum, "and we are looking forward to spending a lot of great time with her."
Santorum collected just half the number of delegates that Romney has. In most states, those delegates can support another candidate of their choice.
After Santorum's announcement, President Obama told supporters in Florida that the November election will provide the biggest contrast in candidates voters have had in decades.