I think it might be more like a business expense report when you travel. If I'm on a business trip and get a coffee, that's a business expense because I'm traveling for the purposes of work. If I'm working from home and go get a coffee, that's not a business expense. Replace business expense with campaign expense and there are likely rules about what a campaign can pay for and what it can't as well as rules around using personal money for campaign expenses, subverting the necessary disclosure rules.

I read a headline just a bit ago that there were 34 counts in the indictment so I'm guessing what they found spans more than a single transaction.