Any minor lapse of political etiquette on the part of Democrats will be blasted over and over by the media for weeks, while major dirty tricks by Republicans will be left to quietly fade away.
Have a look at Harry Reid's account of his first unsuccessful run for the Senate in 1974:
http://books.google.com/books?id=RJoAQgcBNMAC&pg=PT151&lpg=PT151&dq=%22harry+reid%22+laxalt+nun&source=bl&ots=-Xy37JYybz&sig=7yQ-2Mhyp5c75gEKIRpQ6VdmzzM&hl=en&ei=eFdeTuLLM8y1twfwtrmlCw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CC4Q6AEwAw#v=onepage&q&f=falseMy defeat in that overwhelmingly Democratic year can be traced to one crucial mistake that I made. ...
Paul Laxalt had been governor when Howard Hughes materialized in Las Vegas. Laxalt had relaxed the licensing requirements for Hughes, and I suspected that Hughes had in turn feathered Laxalt's nest. I made a real stink about it, insisting that Laxalt's whole family disclose their finances.
To my embarrassment, Laxalt complied. Why yes, he said, my sister the nun who has taken a vow of poverty would be more than happy to inventory her meager finances. It made me look bad, and it taught me another lesson: Go after your opponent as hard as you can. But leave his family out of it.
The anecdote is instructive -- but probably not in the was Reid intended it to be. I think the lesson he and a whole lot of other Democrats took from situations like this one was far broader: It was not to go after your opponent in any way that could possibly be used to make you look bad. And over the years since 1974, the Republicans have become masters of extracting the maximum of outrage from even the most minor slights.
But as I said above, I blame the media for this. It's why Republicans can play the outrage card again and again, while Democrats seems to be helpless to put to rest even the most dubious smears.
When there's a real shitstorm poised to come your way at the slightest provocation, developing more backbone isn't the answer.