In Europe, we still do have formal borders and a “state government” can still impose many rules on its own (despite that, I still consider a political statement about a ban of ICE 20 years down the road as a political BS). Should Germany decide to ban all ICE tomorrow, it can be theoretically done. But I am not sure, how such think could be imposed in Massachusetts,  while Connecticut will still allow ICE on its roads? I guess, they could probably let them travel in and out, just disallow registration of ICE for residents.