When you are in a boxing match, and your opponent is using brass knuckles, you need to use brass knuckles too.
To insist on standing on principle while your opponent has an advantage will more than likely result in a win for your opponent.
Ted Cruz is one of our best possible candidates, and if he wins the nomination, i'm going to work for and support him. If anyone says "he's not a natural born citizen", I will respond "Neither was Obama."
It would be nice if we all followed the rules, but since others won't, we shouldn't be constrained by them either.