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Despite his mantra to stay “positive,” Republican presidential candidate Newt Gingrich took a swipe at rival Ron Paul on Thursday, suggesting that the Texas lawmaker's political base consists of “people who want to legalize drugs.”

During a radio interview with conservative commentator John McCaslin, the former House speaker also said that Paul is naive about the war on terrorism and Iran’s nuclear program. “This is a guy who basically says, if the United States were only nice, it wouldn’t have had 9/11. He doesn’t want to blame the bad guys.… He dismisses the danger of an Iranian nuclear weapon and seems to be indifferent to the idea that Israel could be wiped out. And as I said, I think the key to his volunteer base is people who want to legalize drugs.”

Paul has grown in strength in recent polls in Iowa and is threatening Gingrich’s ability to emerge from the state’s Jan. 3 GOP caucuses as the clear-cut conservative alternative to former Massachusetts Gov. Mitt Romney. Both Paul and Romney have unleashed a barrage of negative ads against Gingrich in the first caucus state, prompting Gingrich to challenge Romney to go one-on-one with him in a debate.

“I’m happy taking the heat, why doesn’t he join me in the kitchen?” Gingrich said on Fox News late on Wednesday, referring to Romney’s quip that his rival should get out of the kitchen if he can’t stand the heat of critical ads. Gingrich called on Romney to join him for a 90-minute debate, a shorter engagement than the three-hour “Lincoln-Douglas” style debates he has touted for several weeks now.