If Obama did do it (and I'm not saying that he did, I'm just floating this for the sake of argument), then he could have done it illegally, i.e. without judicial involvement. Because a politically motivated wiretap wouldn't be legal in the first place, so what sense would it make to involve the judicial circuit for such a thing? And the parties involved could have covered their tracks well enough that a formal legal inquiry wouldn't uncover it with a cursory look.
But no, let's not even consider that possibility on Twitter.
