Soooo.... I have my own answer to your question, but it falls into the category of "things that don't have to be nailed down as long as there are one or more plausible explanations, from which the reader can take your pick."

Basically, John had incomplete information (just as Journey did). Alexandra speculated that the reason John (or who she thought was John) didn't attack her directly was fear of the Circle of Protection. But maybe she was wrong and John didn't know about it. Or maybe he didn't believe in it. Or he was really clever and well-informed and had figured out that Journey had already triggered it. Or he'd been watching other people harass and try to kill Alexandra, and figured that if she still had a Circle of Protection, it should have been triggered by one of her other enemies.

Any of those work for you? If not, I can give you the real reason.

(I'm lying. I won't give you the real reason. But there are clues. :P)