Based on the John Edwards case, if Trump is ever called to answer charges of campaign finance violations, the prosecution would have to prove Stormy Daniels was planning on going public regarding the affair AT THE TIME THE MONEY WAS PAID.
In other words, to be accused of paying hush money for the purposes of assisting his campaign, there has to have been a risk of the negative news coming out had the money not been paid.
"I'm going to tell the NYT we had an affair."
"I'll pay you $130K not to, because it'll ruin me in the election."
"Okay, Mr. Future President."
In all the Cohen reports, I've yet to read that Stormy approached Trump first demanding hush money. Trump had Cohen pay her preemptively.
Since she signed an NDA as required to receive payment, there is evidence (her signature) that she never intended to go public. In fact, she denied the affair multiple times publicly prior to the payment.
Without evidence to the contrary, it's a private payment to avoid embarrassing information from being made public and to avoid marital problems -- not a campaign contribution.
https://blog.harvardlawreview.org/the-coming-storm-hush-money-and-the-federal-election-campaign-act/