Some conservative political groups have run into trouble making ads that criticize Obamacare. The ads were intended to showcase "horror stories" from the Democrats' national health care overhaul, but instead attracted zealous fact-checking and ferocious pushback from liberal activists.The most striking example is a recent ad from Americans for Prosperity, the organization backed by Charles and David Koch, the conservative businessmen-philanthropists who have emerged as this year's Target No. 1 for Democrats.