Eh?
If you're talking about Stephanie Clifford, aka Stormy Daniels, this isn't just about whether a married man committed adultery when his wife had just given birth.
It's the fact that just before the election Trump paid Clifford a large amount of money to stop the (quite old) story becoming public, in case it influenced voters' choice of him. So this was election spending. It appears to be an illegal campaign contribution and appears he broke the law in order to influence the election.
NB Ever chivalrous, first Trump denied paying Clifford, and tried to dump the blame on his now-ex lawyer, Michael Cohen. Then some documentation was revealed and he admitted it.
Stormy Daniels: Trump discloses payment to reimburse lawyer
www.bbc.co.uk/news/world-us-canada-44143960