Actually, voters have no say in who gets to make these prosecutorial decisions, and that’s a huge problem. Unless a prosecutor files a case against someone, there is no case, no matter what they’ve done. Assistant US Attorneys (AUSAs) are the ones making the decisions as to whether or not to file, and they are just lawyers hired through normal recruiting channels. Branch US Attorney offices are little fiefdoms - technically they answer to the head US Attorney in their federal district, but in practice they have little contact with him or her and do as they please unless they really mess something up.
Because people are people, and many of them view the position of AUSA as a stepping stone to $800/hr jobs at white collar criminal defense firms or prestigious political appointments, they tend to file cases with which they can make a name for themselves. One way for them to do that is “creative prosecution” - charging people for conduct that isn’t clearly in violation of a given statute, and then trying to shoehorn the case into a conviction or guilty plea. There is no moral hazard for them in doing this - if they lose, nobody cares, and if they win, they get credit for their genius - so they will do it again and again until it works.
That’s what happened here - they managed to shoehorn a conviction in a highly questionable case, and the AUSAs behind it will ultimately leverage this into a better job and a better life. I’m not sure that voting for individual AUSAs is the answer, but something needs to be done to reign these people in. They currently have free reign to burn lives to the ground for their own gain.