He was in office when she was threatened. He was in office when he lied about it which, given his political power and her far lesser social position, is slander. The payoff is probably illegal on one side or both no matter how or when it happened. If she requested payment to keep quiet, she's broken a law. She's broken a law as a private citizen. He's paid these women for sex. While many of us here don't find that morally wrong, it is illegal. It's illegal and his own platform is for keeping it that way. Using money to cover up illegal activities before taking office or after matters the same. He's broken the law while holding the highest seat in American politics. It's not his business. If we have a President who has the ability to act illegally, that is our business.
Editing to add: I really wasn't singling you out as a laughing it off person. If that was the case, I wouldn't keep talking to you about it even in my bored, too pregnant to move state. Sadly, most of the people I've seen laughing it off are IRL folks for me. People who claim to be evangelical or liberal, "feminist", educated etc but who I'm seeing very clearly do not extend their views to sex workers or blondes with big tits even. Much more heartache inducing than folks here. Not sure about my punctuation use. I'm reasonably educated and thoughtful but nothing fancy.