In John's home state of Mississippi, government regulations concerning your vehicle are blissfully ignored each and every day. In some studies 75% of Mississippi vehicles aren't insured, or lack brake tag certifications, or are driven by the unlicensed. I don't think that it's actually nearly that high currently, but a large chunk of the people one would encounter driving around Mississippi on any given day are either outright breaking the law or not complying with various regulations. What would this mileage tax mean to them? It would just be another law to be ignored. Mississippi may be an extreme example, but the same thing would hold true in most rural and Republican areas. The rural poor in blue states, where enforcement would probably be more exacting, will be hit hardest, also the suburban middle class.
Anyway, America's Gay Robot has a very long way to go to get a mileage tax enacted. For one thing, it's so broadly unpopular that I predict it won't pass the House, much less the Senate. If the Dems shove it into their next taxation bill, it'll poison the bill. They'll try to sneak it in under the radar, but it's such an unpopular concept that there are any number of politicians both local and federal who'll chase popularity by denouncing it and making a stand against it.