Will the wingnuts attack Obama with every vile claim they can invent? Of course. That’s who they are.
But the question isn’t whether the attacks will be made. The question is whether the attacks will stick.
Actually, I don’t think that even Hillary-bashing would work as well this year as it has in the past, simply because voters desperate to get rid of the GOP won’t want to hear anything bad about the Democratic candidate, whoever that might be. Reagan got away with being obviously senile in 1984 because Mondale never made the case that he was a plausible replacement. That’s also how Nixon got away with being obviously Nixon in 1972: as soon as McGovern had been safely disposed of, the media and the political class became ready to believe Watergate. The same sort of cognitive-dissonance effect will help protect whoever is the Democratic nominee this year.
In addition, not all candidates pose equally target-rich environments for vitriol. I think that’s true of Obama as compared to HRC. But let’s take it from our side. It’s predictable that Atrios and Kos and CrooksandLiars (and, of course, your humble obedient servant) will have vicious things to say about this year’s Republican nominee. But consider how much easier it would be, how much more enthusiastic we would be about it, and how much more of our attacks would get through to the voters, if the nominee were Giuliani or Huckabee rather than Romney or McCain or Thompson.
Similarly, on Election Day in November I think that Barack Obama as the nominee would excite far less Republican enthusiasm than would HRC.