MESA: Rivals heaped criticism on surprise front-runner Rick Santorum in a debate among Republican presidential candidates on Wednesday, hoping to stall his surge at a pivotal period in the 2012 campaign.
Mitt Romney, scrambling to fight back against a grave threat from Santorum, went after his chief rival early and often.
He tried to raise enough doubts about Santorum to make up for a deficit in the polls, with Michigan and Arizona to vote on February 28 and set the table for the crucial March 6 "Super Tuesday."
Former Massachusetts Governor Romney repeatedly questioned Santorum's fiscal and social conservative credentials and criticized his time in the U.S. Congress when he was a backer of government spending projects deemed wasteful by critics.
"Don't look at me, take a look in the mirror," Romney told him at one tense juncture when Santorum accused Romney of backing moderate policies in Massachusetts.
Romney put the former senator from Pennsylvania on the defensive for supporting a much-derided $400 million "bridge to nowhere" project in Alaska that was eventually abandoned.
Tempers flared between Santorum and Romney frequently and at one point the two candidates talked over each other, refusing to cede the floor. At times the crowd booed. Debate moderator John King of CNN frequently let the two candidates battle it out.
"When I was fighting for the Olympics, you were fighting for the 'bridge to nowhere,'" Romney told Santorum.
"You don't know what you're talking about," Santorum snapped back. He insisted that earmarks are subjected to public scrutiny and can be useful, although there has been a move among congressional Republicans to ban them.
Santorum needs to build on his momentum going into the Arizona and Michigan primaries on February 28 and pave the way for Super Tuesday. The Republican candidates are vying for their party's nomination to challenge Democratic President Barack Obama in a November 6 general election.
Santorum and Romney are in a close race in Michigan, according to opinion polls, with most recent surveys showing the two divided by 4 percentage points or fewer. A victory in Michigan is critical for Romney as he needs to prove he can win in the state where he was born.