So let me make sure I have this straight. John Edwards, neither serving in office nor currently running for anything, admits to having an affair with a campaign film producer. This is not only the biggest story on the weekend that Russia and Georgia go to war, it is also generally understood to have extinguished whatever future political plans Edwards may have had.
John McCain, sitting senator and presumptive Republican presidential nominee, not only admits to having an affair during his first marriage but actually left his wife and children and married the rich young heiress with whom he was dallying. This is understood to be old news which has no bearing whatsoever on McCain's presidential ambitions.
As I've noted below, I have no interest in what politicians do once they flip the deadbolt on their hotel room doors. Good people do bad things; bad people do good things. I have no idea where Edwards or McCain fits along that continuum. Indeed, the best presidents of the 20th Century have generally been proven philanderers (FDR, LBJ, JFK, Clinton) while the worst (Nixon, Ford, Carter, W.) have generally been considered faithful to their wives, if not (in some cases) to their solemn oath of office.* I'm not saying we should elect tomcats; I'm simply saying that we shouldn't care one way or the other.
But if we're going to make sheet-sniffing a regular feature of our political process, then the same rules ought to apply regardless of how much journalists like or dislike the politician in question.
*Yes, I left out Reagan. I have no idea what his personal history was back in his Hollywood days and I don't think he was an especially good president, a view that was shared by roughly half of all Americans at the time of his presidency.