Michael J. Fox's ad for Democrat Claire McCaskill is moving, and the fact that it's undeniably tough to watch -- a famously boyish American actor suffering the debilitating effects of Parkinson's disease -- probably doesn't weaken its effect as an ad. In fact, in two days on YouTube, it's been watched well over 300,000 times. Fox, a staunch supporter of embryonic stem-cell research, is about as clean-cut, heart-wrenching a spokesman as you could possibly want. Incumbent Rep. Jim Talent, R-Mo., who opposes such research, certainly can't relish being the bad guy here.