Here's the ad, via Jonathan Martin. It's about immigration, predictably. Set to air tomorrow (which is actually today now):

I'm actually in Western Iowa, scheduled to follow Huckabee around today. If the weather holds--and that's a big if; we're slated to get a big ice storm tonight--I'll report back on what he has to say about it.

For the moment, I think Mark Halperin has it more or less right: I don't see this kind of thing is damaging Huckabee much here, because voters don't seem drawn to him over any particular policy position so much as his personality. As long as he keeps it together and continues to act like the guy they fell in love with, he's probably in good shape in Iowa. Then again, these ads may touch a nerve with him, in which case all bets are off...

--Noam Scheiber