Let me guess the other one: There's no way he would be able to clarify his multiple arrests without destroying his relationship with his brother, whom he claims was arrested while using his identity.
(Either that, or the "mistaken identity" stuff is a lot of hooey, and his brother wasn't ready to put himself on the cross for Darrell.)
Issa's arrests would have become Demo cannon fodder in the campaign, and would have derailed him eventually. On the other hand, there are no such charges against McClintock -- the best they've been able to do heretofore is that one of his advisors is too durned Christian.
Issa would also have to fight the notion that he was trying to buy his way into the Governor's mansion -- one that wouldn't be totally inaccurate.