The debate featured just five of those who are campaigning for the Republican presidential nomination -- Arizona Sen. John McCain, former Massachusetts Gov. Mitt Romney, former Arkansas Gov. Mike Huckabee, former New York Mayor Rudy Giuliani and former Tennessee Sen. Fred Thompson.
Romney chastised McCain as "one of two Republicans who voted against the (George W.) Bush tax cuts."
McCain said tax cuts must be accompanied by spending cuts.
Romney also went after Huckabee, claiming the Iowa Caucuses winner raised taxes by $500 million net while he was governor of Arkansas.
"You make up facts faster than you talk so let's slow it down," Romney said, as Huckabee tried to account for his tax policy in Arkansas.
Thompson touted his plan for Social Security reform and said no one in Washington has the ability to alter the debate on Social Security.
Giuliani said he's the only candidate with firsthand experience dealing with an "Islamic terrorist attack."