Ron Paul released a new advertisement late Monday night blasting his primary rivals in the Republican presidential race as "three of a kind," with none as suitable as the Texas congressman to challenge Obama in November.

The commercial pulls few punches, labeling Newt Gingrich a "serial hypocrite," Rick Santorum a "counterfeit conservative" and Mitt Romney a "flip-flopper." The ad argues that support for the individual mandate, bank bailouts and growing the national debt — each articulated in some way by Paul’s rivals — make them too liberal for the GOP nomination.

“Three men, one vision: more big government, more mandates and less freedom," a narrator says.

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“At a time when Republican voters are looking for a true conservative to defeat Obama, this ad effectively makes the case that Newt Gingrich, Rick Santorum and Mitt Romney do not measure up. Ron Paul, in stark contrast, is presented as the one and only authentic conservative in the race,” said Paul campaign chairman Jesse Benton in a statement.

The ad goes on to tout Paul's conservative credentials, including voting against tax increases and federal budgets. It also emphasizes the congressman's anti-abortion and anti-union records, issues the campaign believes will play well among conservatives in South Carolina.

Paul defended his attack ads as fair when pressed by the other candidates during Monday's GOP debate.

“They should be abandoned if you’re not telling the truth, but if you’re exposing a voting record, I think it’s quite proper," Paul said.

He went on to say he had only one concern about attacks on rival Rick Santorum.

“I only had one problem: I couldn’t get all the things in I wanted to say in one minute," Paul said.

Santorum, returning fire, argued that Paul's ads frequently quote left-wing sources.

“Of course left-wing organizations say a lot of bad things about me. I would expect them," Santorum said. "I wear that as a badge of honor, not something that I’m ashamed of.”