GREENVILLE, SC -- Speaking before a breakfast town hall here in South Carolina, new Republican frontrunner Newt Gingrich suggested fellow GOP candidate Michele Bachmann is "factually challenged."

During a brief exchange with reporters, Gingrich was asked about Bachmann's claim that Gingrich's position on illegal immigration amounts to amnesty.  Bachmann criticized Gingrich's statement that he would allow illegal immigrants who have been in the United States for 25 years to remain in the country.

What about Bachmann's criticism?  "Some people are just factually challenged," Gingrich responded.  "It's unfortunate.  When I was a teacher I occasionally had a student who couldn't figure out where things were or what things were or what the right date was.  When that happens, you feel sorry that they are so factually challenged."

"What I will say," Gingrich continued, "is that the voters will be pretty good over time in distinguishing between people who know facts and people who don't know facts…people who are focused on positive, large solutions, not people who are trying to pick fights."

So far in the campaign, Gingrich has pleased Republican audiences with his policy of not attacking rival candidates.  But now that he is the GOP frontrunner, he has become the target of a growing number of attacks from fellow candidates.  In an interview Tuesday night, Gingrich vowed to "keep being positive."  But his words about Bachmann Wednesday morning suggest that might be a tough job.