Staunch conservative Republican Rick Santorum has quit the race to be his party's nominee to run against the incumbent Barack Obama for the US presidency in November. The former Senator for Pennsylvania - where he bowed out on Tuesday, without saying the reason - won 11 states" votes, but polls showed support in his home state was down, and he was seriously trailing frontrunner Mitt Romney. Santorum said: "I know a lot of folks are going to write, maybe even those at the White House, "game over." But this game is a long, long, long way from over. We are going to continue to go out there and fight to make sure we defeat President Barack Obama, that we win the House back, and that we take the United States Senate, and that we stand for the values that make us Americans. God bless you. The Pennsylvania primary is on April 24. Tom Mann, political analyst at Brookings Institution: "If Rick Santorum had any prospect of a victory in Pennsylvania, he would have stayed in because he'd like to stick around and hope for a miracle. It's certainly over now. It'll be officially over once the Republican Convention convenes and Romney is nominated on the first ballot. Santorum did not endorse Romney but he has helped him enough in just dropping out, strengthening the more centrist candidate. Some say this will allow the Republican party to avoid its internal divisions getting somehow worse. Romney will be free to give more attention to a more politically moderate electorate and women voters and the Hispanic community. Competing with Santorum he was able to devote less energy in their direction before. Romney's camp is confident that nomination rivals Newt Gingrich and Ron Paul are just hanging on, and will focus more on the Democrat in the White House. Romney said: "President Obama thinks he's doing a good job. I'm not kidding. He actually thinks he's doing a great job! The wealthy former Massachusetts governor attacks Obama as weak - on the economy, over health care disagreements and weak on American greatness. Obama's campaign manager commented on the Santorum withdrawal saying Romney ran so many negative ads about his opponents it was not a surprise. More about: 2012 Republican primaries, Mitt Romney, Rick Santorum, USA presidential elections 2012