Santorum's sudden announcement came last night, a day after his campaign said that his youngest daughter, Bella, had been hospitalised. This smooths the way for Romney to take on Obama in the November election.
As contours of a straight Obama-Romney fight emerged, a campaign manager for the incumbent President warned the republican challenger against using negative tactics during the campaign.
Obama's manager Jim Messina issued a written statement reacting to Santorum's withdrawal, saying that Romney may have been able to grind down his opponents, but "won't be able to buy the presidency".
In his dropout speech, Santorum did not mention Romney, but his spokeswoman told CNN that "Romney and Santorum had a nice conversation" and "would be talking again." Though Santorum trailed as a distant second in the battle for Republican presidential nomination, he said, "While this presidential race is over for me. We are not done with the fighting" as he pledged to do what he can to defeat the democratic candidate. Santorum quit the race just two weeks before a primary vote in his home state of Pennsylvania, where opinion polls suggested he may lose to Romney.
The Republican National Committee called Santorum's decision to dropout as "commendable". Pressure will now build up on former House Speaker Newt Gingrich to drop out and let the Republicans rally round Romney.
Gingrich has just won the contest in only two states and has acknowledged that Romney was his party's most likely nominee. With this Romney is now all set to be the Republican nominee, even though he is yet to reach the magical figure of 1144 delegates to earn the presidential ticket.
As of now he has 656 delegates. Romney was followed by Santorum with 272 delegates, Newt Gingrich (140) and Ron Paul (67).