In theory, the European governments could always waive reciprocity on their end and continue allowing travel from the US, if that's the biggest thing stopping t

In theory, the European governments could always waive reciprocity on their end and continue allowing travel from the US, if that's the biggest thing stopping them from refusing. On the other hand, that wouldn't leave the US with any "consequence" for not reaching a deal. Note that it's not at all unprecedented for US/Europe/etc travelers to be offered visa-free access without reciprocity for exactly this reason. The whole concept of "passport power" implies there are a lot of countries that give US citizens access without a visa without the US and other countries giving them the same.