I have to differ on the point of view offered here that France could not have been arrested and processed if he was not found behind the wheel of the vehicle. It may be different but I have processed many such impaired drivers in my career for the very same set of circumstances. First off you have a witness that can testify that he was in fact the driver of the vehicle at a specific time and that he was driving in an erratic fashion. It doesn't really matter that he was impaired by alcohol, drug or other, the offence is the same. As far as processing France from his home they could have interviewed him relative to whether he had anything to drink after he got home. He may have said no so now you have no issue with whether he drank after he got home or not. Even if he did and told you he had 2 drinks after he got home you could perform the Breath test and then have an expert extrapolate back his readings at the time of driving. The fact an officer could smell alcohol, you have a witness(s), you have the warm car, etc you are good to go. I can't believe it would be that much different in the States than Canada. I have been successful in getting convictions in court on several similar incidents to this one. I believe they were a little intimidated about who he was and no one wanted to make the decision to proceed.
Cheers, CVOMOE