Hard to see how settling harassment claims have anything to do with campaign finance laws.
Would spending money on defending the claims have been a violation too?
The attempted linkage is that he used campaign funds for the payoff. Their big problem is that Candidate Trump, put far more of his OWN money into the campaign. Therefore, it is a very reasonable argument that Candidate Trump paid the settlement with his own money and not with any donations.
It doesn't, but it has everything to do with harassing and damaging the President.
Only a sick twisted legal-parasite could attempt to fabricate an answer to your question