Santorum suspends campaign, clearing Romney's path NEW: President Obama's campaign immediately targets Mitt Romney The presidential race "is over for me," Rick Santorum says Romney, other Republicans praise Santorum's decision to suspend his campaign A new poll shows Republican front-runner Romney trailing President Obama Washington (CNN) -- Conservative challenger Rick Santorum announced Tuesday that he is suspending his Republican presidential campaign after a weekend of "prayer and thought," effectively ceding the GOP nomination to front-runner Mitt Romney. Santorum made his announcement after the weekend hospitalization of his 3-year-old daughter Isabella, and in the face of tightening poll numbers in Pennsylvania -- the state he represented as a U.S. senator -- ahead of the April 24 primary. "Ladies and gentlemen, we made the decision to get into this race around our kitchen table, against all the odds," Santorum told a news conference, flanked by emotional family members. We made a decision over the weekend that while the presidential race for us is over, and I will suspend my campaign effective today, we are not done fighting. The development means Romney is now the certain GOP nominee to take on President Barack Obama in November, as Santorum was his main challenger. While Romney still needs to win several hundred delegates to clinch the nomination, Santorum's departure from the race leaves his path unhindered. Sources said Santorum called Romney before his announcement, and the two could meet soon. The sources indicated Romney wanted Santorum's endorsement right away, but Santorum's communications director, Hogan Gidley, said there was no guarantee that would happen after what has been a tough and at times bitter campaign. In his remarks Tuesday, Santorum never mentioned Romney by name. Santorum could be a valuable ally for Romney by helping deliver the party's Republican base, which harbors some distrust of the conservative credentials of the former Massachusetts governor. However, Santorum has consistently said the party needed a true conservative candidate -- himself -- to defeat Obama, and he has relentlessly attacked Romney's support for health care reforms in Massachusetts that included a mandate for coverage similar to the 2010 federal health care law despised by conservatives. Romney's difficulty with conservatives was evident Tuesday, as two groups known for right-wing stances on social issues commended Santorum's campaign effort but made no mention of Romney. "Sen. Santorum is an able and worthy competitor, and I congratulate him on the campaign he ran," Romney said in a statement. He has proven himself to be an important voice in our party and in the nation. 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. Former House Speaker Newt Gingrich, another GOP contender trailing well behind Romney and Santorum, also congratulated Santorum for a "remarkable campaign" that showed the appeal of conservative principles. Both Gingrich and the other challenger, Texas Rep. Ron Paul, said they intended to stay in the race to the Republican convention in August. "I think it makes it clearer and simpler," Gingrich said of Santorum's decision while campaigning in North Carolina later Tuesday. There is one conservative voice in the race and then there is a moderate, and I think [that] makes it easier to articulate and to focus on the platform issues I want to focus on. In a statement by his campaign, Gingrich said he "humbly" asked Santorum supporters to check out his conservative record on his website Newt.org. Shortly after Santorum's announcement, the Gingrich website appeared to have crashed, though the reason wasn't known. The Obama campaign immediately took aim at Romney, with campaign manager Jim Messina saying it was "no surprise that Mitt Romney finally was able to grind down his opponents under an avalanche of negative ads." "The more the American people see of Mitt Romney, the less they like him and the less they trust him," Messina said in a statement. While calling himself the 'ideal candidate' for the tea party, he has promised to return to the same policies that created the economic crisis and has alienated women, middle class families, and Hispanic Americans. Santorum advisers including Gidley said the final decision to suspend the campaign, which allows him to continue raising money and probably keep control of delegates won so far, came Monday night and was based on three factors. Santorum needed the Texas primary on May 29, with 154 delegates at stake, to be winner-take-all instead of the proportional allocation system based on vote results now in place. However, a complex process for changing the allocation method made that unlikely, they said. In addition, Santorum needed Gingrich to step aside so Santorum could bring together the conservative right, but Gingrich stayed in the race, they said. Santorum also needed to win Pennsylvania, which remained possible but would require large amounts of time and money against an expected Romney offensive there, the advisers said. Santorum had canceled two events earlier Tuesday while adding an afternoon event that turned out to be his withdrawal announcement. Gidley, the campaign's communications director, said the two morning events were canceled to allow Santorum and his wife, Karen, to "settle in at home" with their young daughter. Santorum mentioned Bella several times in his comments, saying he was inspired by people who cited the need to speak up for people with disabilities and others being marginalized by the nation's present direction and problems. "Against all odds we won 11 states, millions of voters, millions of votes," Santorum said, adding he found a "deeper love for this country" through the campaign. "It was a love affair for me going from state to state and seeing the differences but seeing the wonderful, wonderful people of this country who care deeply about where this country is going in the future, who care deeply about those who are out there paddling alone who are feeling left behind and in some respects are feeling hopeless and want to do something," he said. Meanwhile, a poll Tuesday shows Romney trailing Obama in a head-to-head matchup, though voters remain split on which presidential contender is best equipped to handle the economy. Both margins were within the poll's 3.5 percentage point sampling error. Romney has used a huge advantage in money and organization to build his lead over Santorum, Gingrich and Paul. Gingrich admitted Sunday that Romney was the likely nominee. The goal now for Gingrich and Paul is to prevent Romney from reaching the 1,144-delegate threshold before the convention. CNN's Kevin Liptak, Dana Bash, John King, Peter Hamby, Shannon Travis and Steve Brusk contributed to this report.