Anyone who would be influenced by such strategies has already been influenced. The tabloids are full of it, and have been so for a long time.
But slimy Karl Rove/ Lee Atwater/ 'swiftboating' tactics on a somewhat more sophisticated level could achieve something unpleasant under the wrong circumstances.
Ian Birrell - one of the very few Conservatives who occasionally says something somewhat reasonable - wrote the following about Crosby, which at any rate counteracts the idea that he is some sort of electoral public-relations Superman:
http://www.independent.co.uk/voices/comment/lynton-crosby-is-a-disastrous-signing-for-the-tories-8327050.html