There is no crime unless you broke the payments up to avoid being detected, or you used campaign funds. Trump isn’t the type who personally conducts transfers or such himself....he has accountants to do the simple stuff. I also doubt you can find this linked to any campaign fund. So they are mostly fishing for something that would be illegal.
Now, what they might uncover if they dug real deep....there might be another ‘Stormy’ out there that hasn’t be identified yet. I’m taking the guess that this is their ultimate hope...a second Stormy.
Trump could hand monies to her personally,....it's still not a crime.