Interesting, from National Journal:
So if Thompson does enter the race, who would it hurt? Two recent polls — one by Peter Hart and Neil Newhouse for NBC News and the Wall Street Journal and the other by RT Strategies for the Cook Political Report — indicate that Thompson’s candidacy would draw most from former New York City Mayor Rudolph Giuliani, perhaps about 4 to 6 points. He would draw minimally, if at all, from Sen. John McCain, R-Ariz., and former Massachusetts Gov. Mitt Romney. Thompson would start out behind Giuliani and McCain and about even with Romney.