In today's Politico, John Harris and Jim VandeHei pose the following hypothetical:
Imagine if at the next presidential debate Barack Obama--who is agitated about what he calls Bill Clinton’s misleading criticisms--cocked his head, smiled ruefully and, in Reaganesque “there you go again” tones, said something like this to Hillary Clinton: “You know, I admired some aspects of Bill Clinton’s presidency. But let’s recall that it was precisely these sort of too-cute-by-half statements that caused him to be reprimanded by a federal judge and stripped of his law license. Senator, you may want to go back to those days and that style of politics, but I think most Americans are ready to move on.”
But obviously Obama can't do this. He has to win over partisan Democrats, particularly since most of the upcoming primaries are closed to independents (pdf). It's true there are quite a few Democrats who thought Clinton was sleazy, but it's nowhere near a majority of the party faithful, and most of them are probably already backing Obama anyway.
It's not uncommon to hear Democrats worry that Obama's reluctance to attack Hillary's record proves that he'll be too timid to take on the Republican candidate in the general election. There may be something to this. But consider: there are very, very few actual policy differences between Clinton and Obama large enough to be used as campaign issues (other than her war vote, which he's done his best to emphasize). This leaves him two options. One, he can try to attack Hillary's involvement in the sundry intrigues of the nineties. He's attempted to do this, but if he goes much further than he already has (as Harris and VandeHei suggest he do), he runs the real risk of alienating the very voters he needs.
His second option is to do what she's doing: cherry-pick votes and soundbites and distort them into essentially misleading attacks. So far he's been reluctant to do this. Is this principled or is it weak? That's in the eye of the beholder. But it certainly doesn't prove that he'd be unwilling to attack the Republican candidate in the general election, when there are going to be plenty of legitimate, substantive differences for him to hammer at.