There's a huge difference here. In Clinton's case, it was portrayed as an "us (Dems) vs. them (GOP)" story. Because this is a primary race, there are going to be a lot of Democratic voters who may not care about Kerry's personal life at all -- but we are still early enough in the process that the party still has options to dump a "damaged" candidate.
Perhaps, but if they are going to do so, they need to do it now. We will see in the next few primaries.
This story was leaked by Clinton's sock puppet, General Jack D. Ripper Clark, and confirmed by Dean. So far it has no Republican fingerprints on it.