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