Judging from what has happened in democratic Western European countries (but also in the US in the past, e.g. with E.J. Hoover, Watergate, etc), the idea that the prior president (or his team) would tap a threatening contender's phone sounds pretty much business as usual. As does the fact that everybody will deny it, especially since the law officially forbids it.
They might not have done out of fear of being exposed later. But the reasoning that only what the law says happens is, to this cynic, laughable.