> International borders fall under federal jurisdiction, so I don't think your point is as strong as you think,

Sanctuary cities don't change anything about international borders or who can enter the country, because international borders are federal issues with federal staff. Sanctuary cities refuse to make their local staff spend time and money reporting on immigration status every time they issue a parking ticket. It's not even a states rights question - nobody even suggests that city officials should check if you have paid your federal taxes every time you take to them, but that's not because (normal) people are objecting to a federally run tax system.