ROUGH CUT - NO REPORTER NARRATION Republican front-runner Rick Perry came under heavy fire on Social Security, jobs and his record in Texas in a heated U.S. presidential debate as rivals tried to halt the governor's momentum. Perry, who has soared to the top of opinion polls in the Republican race, renewed his fight with main challenger Mitt Romney over Social Security. They accused each other of frightening seniors about the popular retirement program. Perry's rivals questioned his claims about Texas job creation, his stance on illegal immigrants and an executive order he gave as governor, which he admitted was a mistake, that young girls be vaccinated for a sexually transmitted virus that causes cervical cancer. Perry played defense numerous times, easing back from his earlier comments on Social Security and the Federal Reserve and deflecting where possible. Former U.S. House of Representatives Speaker Newt Gingrich said he was not worried about Romney and Perry frightening seniors "when President Obama scares them every day". Intense dispute erupted between U.S. Representative Ron Paul and U.S. Senator Rick Santorum about a blog posted on Paul's' website, which states: "Though it is hard for many to believe, honest studies show that the real motivation behind the September 11 attacks and the vast majority of other instances of suicide terrorism is not that our enemies are bothered by our way of life. Neither is it our religion, or our wealth. Rather, it is primarily occupation." The lively exchanges and repeated focus on Perry reinforced his growing stature as the candidate to beat in the 2012 race for the nomination to challenge President Barack Obama.