Saying you do not want to trash the opposition is not just a PR exercise, your behaviour needs to reflect your opinions, otherwise you lose all credibitliy. Obama is trying to stand for a different kind of politics, and he has more credibility amongst a certain segment of the US population than more seasoned politicians. He cannot afford to lose the higher moral ground, because that is what he is campaigning on (check out the videos "yes we can" etc...). And in this sense I find it normal that Samantha resigned, as this is a values issue. Integrity comes at a price.