Greenville, South Carolina (CNN) – Newt Gingrich refused to comment on Mitt Romney's stepped-up campaign efforts to directly attack the former House speaker.
After speaking to business leaders in South Carolina's upstate, Gingrich was asked about two high-profile Romney surrogates calling him a "self-aggrandizing," unreliable and untrustworthy leader.
Gingrich, surrounded by a gaggle of reporters, would only say, "We're going to stay positive."
Romney's campaign arranged a conference call between former Sen. Jim Talent, former New Hampshire Gov. John Sununu and reporters Thursday to discuss Gingrich's stance on a conservative plan to overhaul Medicare.
They also challenged the former House speaker's conservative credentials and warned his lack of discipline would aid Democrats as they worked to re-elect President Barack Obama next fall.
Talent, who served under Gingrich in the House of Representatives, said Gingrich was not a trustworthy standard-bearer for the GOP.
"The speaker's running as a reliable and trusted conservative leader," Talent said. "And what we're here to say with reluctance but clearly is that he is not a reliable and trusted leader because he's not a reliable or trustworthy leader."
Sununu embarked on a media tour Thursday to take on the growing threat. On the conference call with reporters Sununu said Gingrich was "self-serving," "self-aggrandizing," and displayed "irrational behavior."
"The off-the-cuff comments for example that Gingrich throws out on occasion is a reflection of the off-the-cuff thinking that he goes through to deal with issues," he said.
Gingrich Press Secretary R.C. Hammond dismissed Sununu's assault on his boss, saying he found it "a little ironic coming from Governor Sununu."
Hammond reiterated their campaign's message of staying positive and said of Gingrich, "I think the American people are getting a very good look at his temperament, his style of leadership, the kind of president he would be, and we'll let that stand for its own judgment."
Meanwhile, the Romney campaign promised to hold more calls contrasting Gingrich and Romney's records in the future.
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