McCain is completely through as soon as the Dems can get a chance to turn their guns on him instead of each other. If you think Bush has some skeletons in the closet that were covered up, wait until the heart-strings start getting pulled on McCain's past.
We can start by the fact that he left his first wife after a disfiguring car accident so he could be with his rich heiress paramour whom he'd been having an affair with while his wife had been raising his 3 kids.
If that story makes it out on Oprah, there isn't a single woman in the country that would vote for him.
That's just for starters, the guy has also been the key "enabler" for Bush torture legislation, all the while proclaiming he was fighting it tooth and nail and being a real "maverick".
McCain really is a W 2.0 Repug toadie, and his record plays that out.
Clinton, likewise, just has too much dirt waiting to get flung. Pretty much every piece of bullshit pulled by Clinton while in office, Hillary had her fingers in the same pie. It won't take much for the Repug campaign to dust off the old Gingrich talking points and kill her in 106 different ways.
Obama needs to be prepared to fight dirty if he gets the nomination. If he lets the Repugs set him up like a cartoon character like they've been doing in previous elections, and not popping the "Captain war hero" bubble around McCain, he'll be sunk. He's chosen to take the "high road" against Hillary's attacks, and it may cost him if he keeps it up.