It’s the money part of it as explained by manofdillon below.

I believe the case against Trump is legitimate. I just can’t believe the person in charge of bringing the case and the DA who appointed that special prosecutor acted in this manner. This is an incredibly important case - it was important that that the people prosecuting it were above board and beyond reproach. Instead, she appointed her ducking booty call, went on vacations with him, and reimbursed him travel expenses in cash.

It absolutely affects the case and puts into peril an incredibly important case that needed to be prosecuted. I just can’t believe neither of them thought this would come back to bite them in the ass.