Ta-Nehisi is right--this is a hardcore ad. But I think it's the kind of ad that surrogates need to run, if only because there's really not enough time for the candidate to pivot and make a positive case for himself at the end. It's a pure attack ad, and frontrunners don't need to run those. Frontrunners stay above the fray and talk about themselves, and let surrogates do the dirty work. Watch the ad, though--it's solid.