This editorial is a good summary of the slander/ad hominem attacks against Obama occurring in this presidential race.
What I am struck by in so much of this election season is how what is forgivable about one's own candidate is unforgivable about the other candidate. For example, if Barack Obama was an adulterer like John McCain (who apparently left the mother of his children for a younger, richer woman), it would undoubtedly be lifted up by McCain supporters as a clue to his character. But since it is their own candidate, McCain's past personal life is ignored - except, of course, for his tour of duty and years of imprisonment in Vietnam.
Similarly, if Obama had been an active member of the U.S. Council for World Freedom, an organization linked to right-wing death squads in Central America, as McCain was for years, surely McCain's supporters would make a big deal about it. If Obama had been one of the Keating 5, as McCain is, you can bet that his opponents would raise questions about his judgement and character.
Of course, it goes both ways. Undoubtedly, supporters of Obama tend to see McCain in the worst possible light. We tend to cut our own candidate some slack, while nitpicking every failure or inconsistency of the other candidate. It is a lot like the bias we have for our own team in sports - it is irrational and often unfair to the other side, and it blinds us to both the good in our neighbors on the other side of the aisle, and to the limitations of those on our side.
All of that said, however, the ad hominem attacks by the GOP and the McCain campaign have crossed the line of honor and decency. I can only hope that the politics of smear do not succeed on election day.