A crook is someone who is dishonest. You don't think someone cheating on their wife is dishonest?

Not playing a game of word association. When accusing a public figure of being a criminal, focus on explicitly illegal, not immoral acts.

The accusation was that he was a crook, not necessarily (or limited to) being a criminal. You don't have to break the law to be a crooked person, a "crook".

I find that people say it is dishonest when they otherwise oppose the person doing it, and normal minor things not to worry about if they agree with that person.