That is huge if the state can establish that he actually forgot him once before. If so, there is NO EXCUSE for it to happen again. NONE. He did nothing to prevent it from happening again, like a post it note, or the baby bag in front seat, or his briefcase in the back seat, etc.
Right. Though that could be explained along the lines of RH forgetting to pick him up from Daycare at a certain time, where Cooper is in a safe environment.
That they had this particular 'conversation' only the day before, speaks volumes to me.