I found that via HotAir, which also referenced an Elizabeth Wurtzel column that I clicked through to:
Apparently, back when he was running for state senate, Barack Obama had fund-raising events at the home of Bill Ayers and Bernardine Dohrn, and there's been some press about the senator's friendship with this controversial Weathercouple. Many reporters are well aware, even though Mr. Obama has described his connection to Ayers and Dohrn as "flimsy," that the senator's relationship with his radical Hyde Park neighbors is actually quite warm, even close.
In her tepid, wobbling way, Hillary Clinton has attempted to use this well-known fact to portray her opponent as a secret subversive. But mostly, the press doesn't want to touch this story – and no one else does either, as if it actually were TNT. Perhaps right-wing evildoers are holding onto this story to exploit in the general election.
I would add that Hillary had no standing to make this an issue, as her husband, in order to promote her Senate campaign, pardoned a variety of terrorists, from the FALN to, you guessed it, two members of the Weather Underground. So its lack of traction in the primaries wasn't because it was not a legitimate issue then, it's just that Obama, smartly, replied to the effect that if these people were so bad, why did your husband pardon them? That doesn't mean that it's not a legitimate issue now, or that Obama can offer the same rejoinder, as it would be a non-sequitur.
Senator McCain: do you have your list of questions to ask Obama to his face ready for Wednesday night?