Maybe because the haloed one’s Chicago roots have an October Surprise to conclusively rebut these accusations and make those involved in spreading them look, not only foolish, but deceitful and vindictive. Creating a backlash against McCain, who will be blamed, and creating a groundswell of sympathy for the haloed one before Election day.
In other words don't attack because the other side may do what? Fight back? So what? That's a strategy for cowards and fools. McCain won't be tied to it anyway because he has no intentions of attacking him in this area nor does he need to. That's what teams and surrogates are all about.
I say attack on all fronts with anything and everything. Its called politics.