Hillary Clinton's team already tried this "scare-them-stiff" approach. Directly through ads and indirectly through political rumor machines, all these nasty Obama rumors were unleashed during the Democratic primary by a Democratic opponent. And it didn't work.
Democrats have been trying to use this "fearmonger" trope -- mostly against George W. Bush -- for too long now. In essence, they're fighting the last war over and over again. And it hasn't worked out very well for them. Nevermind that if we want to talk fearmongering, Democratic candidates spend a lot of time telling small children that mommy's car is killing polar bears and the earth is going to be drowned by tsunamis shortly before melting. Fearmongering is used by both parties. Sometimes it works, sometimes it doesn't. Meta-fearmongering (accusing the other side of spreading fear) doesn't interest voters and it doesn't work. It's a too-clever-by-half attempt to take certain issues off the table. If you even talk about war, it's fearmongering. Voters want to hear about a candidate's approach to these issues. Meta-fearmongering is the lazy way out and basically an admission that you don't have an answer to counter the fear being mongered.
I only wish Huffington would have taken the question a little more seriously from a McCain camp perspective. There's no doubt she's partially right. There are groups out there spreading a lot of manure about Obama's past. Even the New Yorker (just joking). But that's not McCain's actual team. What does McCain have to do to win?
Team McCain is already doing some of it, by hammering Obama on his objection to off-shore oil drilling. They can also go after Obama for publicly saying the surge would never work. Neither of those has anything to do with terrorists and bombs going off, or rumors that Obama is a secret Muslim with ties to Hamas.
And an inspirational campaign may be the best way to "counter fear" (whatever that means), but Obama's been running an inspirational campaign for almost a year now. He's got that part nailed down. Fear or not, once McCain starts throwing specifics, Obama's going to have to answer back--and he'll have to do it without seeming peevish. Inspirational messages about "change" aren't going to cut it.
Of course, Obama's plenty capable of doing all of that. The guy came out of Chicago, so no one should worry about him being able to defend himself from Republican fearmongers.