Just a quick word on the Harry Reid controversy: generally, stuff like this is used as an excuse to get rid of people that were in trouble with their own supporters in the first place. By all accounts, the Bush White House and many conservatives wanted Trent Lott out, so when he had a little kerfuffle, they stood aside and let him fall. As far as I know, the Obama White House is perfectly happy with Reid, as are (against as far as I can tell) virtually all Democratic Senators. They're all sticking with him. The only people who are not happy with Reid are outside liberals, and guess what? They're the one's calling for Reid to leave.
You might notice what's not so important: what offensive thing was said (and how offensive it really was), and what the other party does. I suppose at the extremes perhaps that's not quite true, but generally, the determining factor is entirely whether the malefactor's supporters stick with him or her or not, and usually that will depend on things other than the particular offense.