Well, I think he could actively campaign while not actively campaigning against her, but I'm inclined to agree with zoe that there might be questions of sexism if he were to completely ignore her.  I think you're right and wrong depending upon the state, and it goes back to that whole "frontrunner" thing, where you don't address your opponent unless you have to.  Tough call.

Conservatives want live babies so they can raise them to be dead soldiers. - George Carlin

Which leaves him in the interesting position that not to ignore a candidate because she's a woman makes him a sexist pig.

I don't think he has to do it at that level. That's what she wants him to do, trouble is he just doens't have to. She's an irrelevance and all he has to do is start attacking McCain. After all, it was Clinton who said what a great and experienced guy McCain was, to the extent that Rachel Maddow said she was fishing for a VP slot. So attacking McCain and republican politics is attacking Clinton and Obama can frame it like that.

keep to the Fen Causeway